For extrapolation to be conceptually plausible, I imagine "knowledge" and "intelligence level" to be independent variables of a mind, knobs to turn. To be sure, this picture looks ridiculous. But assuming, for the sake of argument, that this picture is realizable, extrapolation appears to be definable.

Yes, many religious people wouldn't want their beliefs erased, but only because they believe them to be true. They wouldn't oppose increasing their knowledge if they knew it was true knowledge. Cases of belief in belief would be dissolved if it was known that true beliefs were better in all respects, including individual happiness.

Coherence, one way or another, is unlikely to exist. Humans want a bunch of different things...

Yes, I agree with this. But, I believe there exist wishes universal for (extrapolated) humans, among which I think there is the wish for humans to continue existing. I would like for AI to fulfil this wish (and other universal wishes if there are any), while letting people decide everything else for themselves.