Agreed, you need something like a basement to get a baseline, at the very least a logical basement as a Schelling point. There's not a non-circular obvious decision theoretic reason why you or why cosmological natural selection would 'pick' the squared modulus as a Schelling point. But it's sort of like property rights; we emerged out of Hobbesian anarchy somehow, and that somehow can be at least partially "explained" with game theory, social psychology, or ecology. Ultimately those all feed into each other, but I wouldn't consider it fruitless to choose one approach and see how far it takes you. Does this analogy fail in the case of deriving the Born rule?
If you had said
Deviations from the Born rule should be derived from timelessness-cognizant game theory for multipartite systems in order to find equilibria from first principles.
that would make more sense to me, though I still don't believe that timeless equilibria have much to do with anything. The relationship between simulatee and simulator is completely asymmetric, the simulatee is at the mercy of the simulator in the Vast majority of cases.
As for the origin of the Born rule itself, I certainly don't believe it has an origin in terms of multivers...
These are extracts from some Facebook comments I made recently. I don't think they're actually understandable as is—they're definitely not formal and there isn't an actual underlying formalism I'm referring to, just commonly held intuitions. Or at least intuitions commonly held by me. Ahem. But anyway I figure it's worth a shot.
A proposal to
rationalizederive magick and miracles from updateless-like decision theoretic assumptions:(On Google+ I list my occupation as "Theoretical Thaumaturgist". ;P )