Oh yes, it sounds like I did misunderstand you. I thought you were saying you didn't understand how such a thing could happen in principle, not that you were skeptical of the currently popular models. The classes U and F above, should something like that ever come to pass, need not be AIXI-like (nor need they involve utility functions).

I think I'm hearing that you're very skeptical about the validity of current toy mathematical models. I think it's common for people to motte and bailey between the mathematics and the phenomena they're hoping to model, and it's an easy mistake for most people to make. In a good discussion, you should separate out the "math wank" (which I like to just call math) from the transfer of that wank to reality that you hope to model.

Sometimes toy models are helpful and some times they are distractions that lead nowhere or embody a mistaken preconception. I see you as claiming these models are distractions, not that no model is possible. Accurate?