This sounds like a cool idea, thanks for doing it!
One place where you could find a bunch of ideas is my Database of existential risk estimates (context here). It could be interesting to put very similar questions/statements on Metaculus and see how their forecasts differ from the estimates given by these individuals/papers (most of whom don't have any known forecasting track record). It could also be interesting to put on Metaculus:
- questions inspired by (but different from) the statements in that database
- questions inspired by what you notice there aren't any statements on
- e.g., neglected categories of risks, or risks where there are very long time-scale estimates but nothing for the next few decades
- I think authoritarianism and dystopias are examples of that
- e.g., neglected categories of risks, or risks where there are very long time-scale estimates but nothing for the next few decades
- questions that could serve as somewhat nearer-term, less extreme proxies of later catastrophes
On the other hand, forecasting existential risks (or similar things) introduces other challenges aside from being (usually) long-range. So this might not be the ideal approach for your specific goals - not sure.
(This is a somewhat lazy response, since I'm just pointing in a direction rather than giving specifics, but maybe it could still be helpful.)

I have a doc on my computer with some notes on Metaculus questions that I want to see, but either haven't gotten around to writing up yet, or am not sure how to operationalize. Feel free to take any of them.
Giving now vs. later parameter values
Open research questions
"By 2040, there will be a broadly accepted answer on how to construct a rank ordering of possible worlds where some of the worlds have a nonzero probability of containing infinite utility."
"In 2121, it will be broadly agreed that, all things considered, donations to GiveDirectly were net positive."
"By 2040, there will be a broadly accepted answer on what prior to use for the lifespan of humanity." see https://forum.effectivealtruism.org/posts/XXLf6FmWujkxna3E6/are-we-living-at-the-most-influential-time-in-history-1
"By 3020, a macroscopic object will be observed traveling faster than the speed of light."
Finance
For this, would you prefer to condition on something like there being no transformative AI, or not? I feel like sometimes these questions end up dominated by considerations like this, and it is plausible you care about this answer only conditional on something like this not happening.
The question is intended to look at tail risk associated with stock markets shutting down. Transformative AI may or may not constitute such a risk; for example, the AI might shut down the stock market because it's going to do something far better with people's money, or it might shut down the market because everyone is turned into paperclips. So I think it should be unconditional.
That's in pending now, as are a few other questions you may be interested in, though not identical to the ones you list.
I'll post a response here in a few weeks once most of the questions I intend to write are actually live with a summary.
Thanks for these!
Just to be clear, you specifically mean to exclude not-yet-EAs who set up DAFs in, say, 2025?
It might be interesting to have forecasts on the amount of resources expected to be devoted to EA causes in the future, e.g. by more billionaires getting involved. This could be useful for questions like "how fast should Good Ventures be spending their money?" if we expect to have 5 more equally big donors in 2030 that might suggest they should be spending down faster than if they are still expected to be the biggest donor by a wide margin.
Yes, the intention is to predict the maximum length of time that foundations and DAFs created now (or before now) can continue to exist.
Agreed.