Thanks!

That paragraph was not intended to connote that I know of no promising solutions, but rather to build intuition for the fact that the Legg-Hutter metric does not capture a literal ideal. When someone believes that the Legg-Hutter metric is all you need to measure an agent's intelligence, then it's difficult to motivate alternative proposals (such as your own).

That said, I still need to take a bit more effort to understand your updateless metric, and this is something I hope to do in the near future.