Maybe I'm missing something, but I'm not too impressed by this. It seems like exactly the sort of thing that Eliezer was talking about in "Against Modal Logics" — putting all our confusion into irreducible modal operators and using deductive reasoning to move those boxes of confusion around, instead of actually reducing any of the things we're trying to talk about. What metaethical claims are even being made in this paper, other than the rather obvious desiderata on page 5?