Surely if you were God you would be able to instantly work out BB(n) for any n, which would make you uncomputable, which would indeed mean the Solomonoff prior assigns you being God a probability of zero.

I agree that the Solomonoff prior isn't going to give positive probability to me having any sort of halting oracle. Hmm, I'm not sure whether inferring someone's utility function is computable. I suppose that inferring the utility function for a brain of fixed complexity when arbitrarily large (but still finite) computational capacity can be brought to bear could give an arbitrarily close approximation, so the OP could be revised to fix that. It presently doesn't seem worth the effort though -- the added verbage would obscure the main point without adding anything obviously useful.