Thanks, this is an important result showing that the dominating property really isn't enough to pick out a prior for a good agent. I like your example as a to-the-point explanation of the issue.

I think the post title is a somewhat misleading, though: it sounds as though differences in instantiations of AIXI don't really matter, and they can all be arbitrarily stupid. Any chance of changing that? Perhaps to something like "Versions of AIXI can be arbitrarily stupid"?