Interesting. Easily enough ideas here for a top-level post (certainly for the discussion area.)
I don't know the explanation of QM, but I can say that MWI is false because relativity is true, and MWI requires objective simultaneity.
Not really. I suspect that what you're referring to as "MWI" contains the idea that, in addition to a wavefunction evolving unitarily under the Schrödinger equation, there are also ontologically primitive "branches" (or "worlds") which "split". I think this is obviously wrong. (However, note that the SEP article only says that it's "unclear" how to formulate it in such a way as to be compatible with SR). "Branches" are just patterns that emerge when you zoom out to the macro-scale, in much the same way as fluids with thermodynamic attributes such as temperature and entropy only make sense at the macro-scale. In fact, there's a close connection here - the fact that branches "split" but do not "merge" and the second law of thermodynamics are two manifestations of a single underlying principle.
So why go on thinking that the simulation of Permutation City involves Permutation City actually existing, however briefly, in the universe where the simulation is occurring?
I would interpret the statement "Permutation City actually exists in universe U, which is simulating it" along the following lines: "There is a system in U whose components are causally related to one another in such a way as to be isomorphic to the primitive constituents of Permutation City and their causal relations." (Yeah yeah, at some point I might be called on to explain what I mean by "causal relations" and "primitive constituents", and these are thorny questions, but let's save them for another day.)
So for me "Permutation City actually exists in universe U, which is simulating it" means no more and no less than "Universe U is simulating Permutation City." Or perhaps clearer: once it's established that U is simulating V, there's nothing more to be said about whether V exists in U.
Of course, you won't be happy with this - you want to say (a) that there's either something it's like or nothing it's like to be a simulated human and (b) that actually there's nothing it's like - simulated people are "zombies".
I may as well give the Standard Reply from my camp, though you've heard it all before: "If 'something it's like' is interpreted in the informal everyday sense where 'access consciousness' and 'phenomenal consciousness' are not conceived of as separate, then yes absolutely there's something it's like. Moreover, to the extent that the question carries ethical 'weight', again the answer must be yes. But when you try to do fractional distillation, separating out the pure P-consciousness, and ask whether simulated people are P-conscious, then the question loses all of its meaning."
Permutation City is an awesome novel that was written in 1994. Even if the author, Greg Egan, used a caricature of this community as a bad guy in a more recent novel, his work is still a major influence on a lot of people around these parts who have read it. It dissolves so many questions around uploading and simulation that it's hard for someone who has read the book to talk about simulationist metaphysics without wanting to reference the novel... but doing that runs into constraints imposed by spoiler etiquette.
So go read Permutation City if you haven't read it already because it's philosophically important and a reasonably fun read.
In the meantime, if you haven't then you should also read A Fire Upon The Deep by Vernor Vinge (of "singularity" coining fame) and then read Eliezer's fan fic The Finale of the Ultimate Meta Mega Crossover which references both of them in interesting ways to make substantive philosophical points and doesn't take too long to read.
In the comments below there will be discussion that has spoilers for all three works.