Interesting ideas! I've read your post Interstellar travel will probably doom the long-term future with enthusiasm and have had similar concerns for some years now. Regarding your questions, here are my thoughts:

1. Probability of s-risk I agree that in a sufficiently large space civilization (that isn't controlled by your Governance Structure), the probability of s-risk is almost 100% (but not just from digital minds). Let's unpack this: Our galaxy has roughly 200 billion stars (2*10^11). This means 10^10 viable settleable star systems at least. A dyson swarm around a sun-like start could conservatively support 10^20 biological humans (Today, we are 10^10 and this number was extrapolated from how much sunlight is needed to sustain on human with conventional farming). 80k defines an s-risk as "something causing vastly more suffering than has existed on Earth so far". This could easily be "achieved" even w/o digital minds if just one colony out of the 10^10 decides they want to create lots of wildlife preserves and their dyson swarm consists of mostly those. With around 10^10 more living area as on Earth and as many more wild animals, one year would go buy around this star and the cumulative suffering experienced by all of them would exceed the total suffering from all of Earth's history (with only ~ 1 billion (10^9) years of animal life). This would not necessarily mean that the whole galactic civ was morally net bad. A galaxy with 10,000 hellish star systems, 10 million heavenly systems and a 10 billion rather normal but good systems would still be a pretty awesome future from a total utility standpoint. My point is that s-risk being defined in terms of Earth suffering becomes an increasingly low bar to cross the larger your civilization is. At some point you'd have to have insanely good "quality control" in every corner of your civilzation. This would be analogous to having to ensure that every single one of the 10^10 humans today on earth is happy and never gets hurt even once. That seems like a bit too high a standard to have for how good the future should go.

But that nitpick aside, I currently expect that a space future without some kind of governance system you're describing still has a high chance of ending up net bad.

2. How to create the Governance Structure (GS) Here is my idea how this could look like: A superintelligence (could also be post-human) creates countless identical but independent GS copies of itself that expand through the universe and accompany every settlement mission. Their detailed value system is made virtually unalterable, built to last for trillions of years. This I think, is technically achieveable: strong copy-error and damage protections, not updatable via new evidence, strongly defended against outside manipulation attacks. The GS copies largely act on their own in their respective star system colony but have protocols in place on how to coordinate in a loose manner across star systems and millions of years. I think this could work a bit analogous to an ant colony: Lots of small, selfless agents locally interacting with on another; everyone has the exact same values and probably secure intra-hive communication methods; They could still mount an impressively coordinated galactic response to say a von Neumann probe invasion. I could expand further on this idea if you'd like.

3. Point of no-return I'm unsure about this. Possible such points: a space race gets going in earnest (with geopolitical realities making a Long Reflection infeasible), the first ASI is created and it does not have the goal of preventing s- and x-risks, the first (self-sustaining) space colony gets political independance, the first interstellar mission (to create a colony) leaves the solar system, a sub-par, real-world implementation of the Governance Structure breaks down somewhere in human-settled space.

My current view is still that the two most impactful things (at the moment) are 1) ensuring that any ASI that gets developed is safe and benevolent, 2) improving how global and space politics is conducted. Any specific "points of no-return" seem to me like very contingent on the exact circumstances at that point. Nevertheless, thinking ahead about what situations might be especially dangerous or crucial, seems like a worthwhile persuit to me.

probably near 100% if digital sentience is possible… it only takes one

Can you expand on this? I guess the stipulation of thousands of advanced colonies does some of the work here, but this still seems overconfident to me given how little we understand about digital sentience.

All the things you mentioned aren’t uniquely evidence for the simulation hypothesis but are equally evidence for a number of other hypotheses, such as the existence of a supernatural, personal God who designed and created the universe. (There are endless variations on this hypothesis, and we could come up endless more.)

The fine-tuning argument is a common argument for the existence of a supernatural, personal God. The appearance of fine-tuning supports this conclusion equally as well it supports the simulation hypothesis.

Some young Earth creationists believe that dinosaur fossils and other evidence of an old Earth were intentionally put there by God to test people’s faith. You might also think that God tests our faith in other ways, or plays tricks, or gets easily bored, and creates the appearance of a long history or a distant future that isn’t really there. (I also think it’s just not true that this is the most interesting point in history.)

Similarly, the book of Genesis says that God created humans in his image. Maybe he didn’t create aliens with high-tech civilizations because he’s only interested in beings with high technology made in his image. 

It might not be God who is doing this, but in fact an evil demon, as Descartes famously discussed in his Meditations around 400 years ago. Or it could be some kind of trickster deity like Loki who is neither fully good or fully evil. There are endless ideas that would slot in equally well to replace the simulation hypothesis.

You might think the simulation hypothesis is preferable because it’s a naturalistic hypothesis and these are supernatural hypotheses. But this is wrong, the simulation hypothesis is a supernatural hypothesis. If there are simulators, the reality they live in is stipulated to have different fundamental laws of nature, such as the laws of physics, than exist in what we perceive to be the universe. For example, in the simulators’ reality, maybe the fundamental relationship between consciousness and physical phenomena such as matter, energy, space, time, and physical forces is such that consciousness can directly, automatically shape physical phenomena to its will. If we observed this happening in our universe, we would describe this as magic or a miracle. 

Whether you call them "simulators" or "God" or an "evil demon" or "Loki", and whether you call it a "simulation" or an "illusion" or a "dream", these are just different surface-level labels for substantially the same idea. If you stipulate laws of nature radically other than the ones we believe we have, what you’re talking about is supernatural. 

If you try to assume that the physics and other laws of nature in the simulators’ reality is the same as in our perceived reality, then the simulation argument runs into a logical self-contradiction, as pointed out by the physicist Sean Carroll. Endlessly nested levels of simulation means computation in the original simulators’ reality will run out. Simulations at the bottom of the nested hierarchy, which don’t have enough computation to run still more simulations inside them, will outnumber higher-level simulations. Since the simulation argument says, as one of its key premises, that in our perceived reality we will be able to create simulations of worlds or universes filled with many digital minds, but the simulation hypothesis implies this is actually impossible, then the simulation argument’s conclusion contradicts one of its premises.

There are other strong reasons to reject the simulation argument. Remember that a key premise is that we ourselves or our descendants will want to make simulations. Really? They’ll want to simulate the Holocaust, malaria, tsunamis, cancer, cluster headaches, car crashes, sudden infant death syndrome, and Guantanamo Bay? Why? On our ethical views today, we would not see this as permissible, but rather the most grievous evil. Why would our descendants feel differently? 

Less strongly, computation is abundant in the universe but still finite. Why spend computation on creating digital minds inside simulations when there is always a trade-off between doing that and creating digital minds in our universe, i.e. the real world? If we or our descendants think marginally and hold as one of our highest goals to maximize the number of future lives with a good quality of life, using huge amounts of computation on simulations might be seen as going against that goal. Plus, there are endlessly more things we could do with our finite resource of computation, most we can’t imagine today. Where would creating simulations fall on the list? 

You can argue that creating simulations would be a small fraction of overall resources. I’m not sure that’s actually true; I haven’t done the math. But just because something is a small fraction of overall resources doesn’t mean it will be likely be done. In an interstellar, transhumanist scenario, our descendants could create a diamond statue of Hatsune Miku the size of the solar system and this would take a tiny percentage of overall resources, but that doesn’t mean it will likely happen. The simulation argument specifically claims that making simulations of early 21st century Earth will interest our descendants more than alternative uses of resources. Why? Maybe they’ll be more interested in a million other things.

Overall, the simulation hypothesis is undisprovable but no more credible than an unlimited number of other undisprovable hypotheses. If something seems nuts, it probably is. Initially, you might not be able to point out the specific logical reasons it’s nuts. But that’s to be expected — the sort of paradoxes and thought experiments that get a lot of attention (that "go viral", so to speak) are the ones that are hard to immediately counterargue.

Philosophy is replete with oddball ideas that are hard to convincingly refute at first blush. The Chinese Room is a prime example. Another random example is the argument that utilitarianism is compatible with slavery. With enough time and attention, refutations may come. I don't think one's inability to immediately articulate the logical counterargument is a sign that an oddball idea is correct. It's just that thinking takes time and, usually, by the time an oddball idea reaches your desk, it's proven to be resistant to immediate refutation. So, trust that intuition that something is nuts. 

I would not describe the finetuning argument and the Fermi paradox as strong evidence in favour of the simulation hypothesis. I would instead say that they are open questions for which a lot of different explanations have been proposed, with the simulation offering only one of many possible resolutions. 

As to the "importance" argument, we shouldn't count speculative future events as evidence of the importance of now. I would say the mid-20th century was more important than today, because that's the closest we ever got to nuclear annihilation (plus like, WW2). 

I've thought about this a lot too. My general response is that it is very hard to see what one could do differently at a moment to moment level even if we were in a simulation. While it's possible that you or I are alone in the simulation, we can't, realistically, know this. We can't know with much certainty that the apparently sentient beings who share our world aren't actually sentient. And so, even if they are part of the simulation, we still have a moral duty to treat them well, on the chance they are capable of subjective experiences and can suffer or feel happiness (assuming you're a Utilitarian), or have rights/autonomy to be respected, etc.

We also have no idea who the simulators are and what purpose they have for the simulation. For all we know, we are petri dish for some aliens, or a sitcom for our descendents, or a way for people's minds on colony ships travelling to distant galaxies to spend their time while in physical stasis. Odds are, if the simulators are real, they'll just make us forget about whatever if we finally figure it out, so they can continue it for whatever reasons.

Given all this, I don't see the point in trying to defy them or doing really anything differently than what you'd do if this was the ground truth reality. Trying to do something like attempting to escape the simulation would most likely fail AND risk getting you needlessly hurt in this world in the process.

If we're alone in the sim, then it doesn't matter what we do anyway, so I focus on the possibility that we aren't alone, and everything we do does, in fact, matter. Give it the benefit of the doubt.

At least, that's the way I see things right now. Your mileage may vary.

(d) might be interesting to read

The space industry is well-funded and already cares a lot about demonstrating impact (using a broader definition of impact than EA) to justify its funding, so (a)-(c) might be possible with industry support, and to some extent already exists. 

I think the overarching story behind (f) is relatively uncomplicated particularly in the context of ongoing trade between Russia and Ukraine-supporters over oil etc : Roscosmos continued to collaborate with NASA et al on stuff like ISS because agreements remained in place and were too critical to suspend. Russia was never actually part of ESA and I suspect many people would have preferred it if Roscosmos was kicked off projects like ExoMars earlier. Probably helps that the engineers and cosmonauts on both sides are likely a good deal more levelheaded than Dmitry Rogozhin, but I don't think we'll hear what went on behind closed doors for a while...

Hey Jordan, I work in the space sector and I'm also based in London. I am currently working on a Government project assessing the impact of space weather on UK critical national infrastructure. I've written a little on the existential risk of space weather, too, e.g. https://forum.effectivealtruism.org/posts/9gjc4ok4GfwuyRASL/cosmic-rays-could-cause-major-electronic-disruption-and-pose

I'll message you as it would be good to connect!