If what you say is easily verifiable by consulting mathematicians then
you've just dramatically strengthened the case for the C-Prize.  A
philanthropist can have a trusted consultant verify Hutter's proof and
the C-Prize's salience to it.  The only remaining question is whether
the C-Prize is properly administered -- something the philanthropist
can verify with a combination of business and engineering consultants.

I had run across Hutter's AIXI paper before, when searching for
Solomonoff's algorithmic probability theory, but I read just the
abstract and didn't have the background for it so I sent it off to a
friend who is a doctoral candidate in statistical mechanics to review.
Being a doctoral candidate he doesn't have much time left to review
papers ourside his area so I never got the low-down you just gave.
Thanks for the clear synopsis.

A proof like this should have been available to researchers from the
1960s work on minimum length description (AP, KC, etc.) and decision
theory but apparently no one bothered to put 2 and 2 together for what
-- 40 years now?

This is going to be a major question for science historians:

Why did the AI community fail to formalize this proof for so long?

Given Moore's Law originated at about that time, 40 years ago, there's
a good argument that this ranks as one of the greatest losses of
potential to befall humanity.