Together with Eliezer's idea that agents who know each other's source code ought to play cooperate in one-shot PD, doesn't it imply that all sufficiently intelligent and reflective agents across all possible worlds should do a global trade and adopt a single set of preferences that represents a compromise between all of their individual preferences?

It does, and I discussed that here. An interesting implication that I noticed a few weeks back is that an UFAI would want to cooperate with a counterfactual FAI, so we get a slice of the future even if we fail to build FAI, depending on how probable it was that we would be able to do that. A Paperclip maximizer might wipe out humanity, then catch up on its reflective consistency, look back, notice that there was a counterfactual future where a FAI is built, allot some of the collective preference to humanity, and restore it from the info remaining after the initial destruction (effectively constructing a FAI in the process). (I really should make a post on this. Some of the credit due to Rolf Nelson for UFAI deterrence idea.)