So given some data, to determine the relative probability of two competing hypotheses, we start from the ratio of their prior probabilities, and then multiply by the ratio of their likelihoods. If we restrict to hypotheses which make predictions "within our means"---if we treat the result of a computation as uncertain when we can't actually compute it---then this calculation is tractable for any particular pair of hypotheses.

...

When two people disagree about the relative complexity of two hypotheses, it must be because that hypothesis is simpler in one of their languages than in the other.

This is a fairly minor point, but do you mean to imply that the prior probability of a never-happened-before-event normally swamps out updates about it's probability that you find out later on? Or that people update to information by reformulating their concepts so as to express more probable events to have lower complexity?

Either of those would be very interesting, though I also think the argument would stand if you didn't mean either of those as well.