Re: But what about the cat?
"But cats are pretty cool already, no?"
Er, yes and no.
"The experiment will be easiest to run if the probabilities are equal -- so the bags are equally warm, comfortable, easy to get into, hard to be pulled from, inconvenient for whichever human is nearby, on top of something someone is wanting to read, etc."
I also think that it's going to be impossible to get two exact bags and even if there is only an infinitesimal difference between them the cat will choose the best one
"if we cool the cat down as far as possible."
I think you are probably breaking the 5th Law of Thermodynamics
" Any small increase in the cat's de Broglie wavelength will be extremely helpful."
Cats can adjust their de Broglie wavelength, their zero point energy and almost every other parameter. They are also quite capable of emerging from a blackhole ( or any other sort of interesting subterranean space)
All this off-topic for sure but discussing GR at this time of the morning (UK) is a bit heavy.