Mill's point that happiness might derive from having intrinsic goals other than happiness is interesting; I do find it hard to imagine having this feeling though:

In this frame of mind it occurred to me to put the question directly to myself: "Suppose that all your objects in life were realized; that all the changes in institutions and opinions which you are looking forward to, could be completely effected at this very instant: would this be a great joy and happiness to you?" And an irrepressible self-consciousness distinctly answered, "No!"

I personally am quite confident I would experience "a great joy and happiness" if some reform happened e.g. factory farming ended at this moment, and I find it hard to imagine this not being the case. But as you suggest, this may be more likely to occur at a certain "development point" I've not reached yet unlike Mill.

Nor has it ever been the case for me that "My conception of my own happiness was entirely identified with this object [of being a reformer of the world]". Though I do often wish, on a meta-cognitive level, that my happiness (which seems like almost the same thing as my "conception of my own happiness") was much further in that direction, because then I would work much harder on doing good, even if burnout like this becomes a bit more of a risk.

I notice that one of the UK grants for alernative proteins which you cite says, "Cultured meat, insect-based proteins and proteins made by fermentation" (my emphasis). I find this quite concerning.

I didn't previously realise the term "alternative proteins" includes insects. Has this always been the case? Is the definition contested or is a different term needed?

From the NAPIC website, they include Entocycle, "a world-leading provider of insect farming technology", as one of their partners (though this may not be representative). Interestingly Entocycle do have two pages on insect welfare. 

My weak intuition is that pro-life people would support anesthesia. For one reason, they may support it precisely because of the reason you give that pro-choice people do not support it (that is, the implications of moral personhood some people may infer). On the other hand, one counterexample to my intuition is the analogy to how some animal rights activists oppose welfare reforms or at least discuss them with a negative tone, due to a more absolutist or anti-incrementalist position. 

But perhaps more importantly, if it's true that pro-life people generally would support it, I would expect that to make it less tractable, because there's a risk pro-choice people would react and be polarised against it if it was seen as a pro-life political weapon.