[ blahblah :) ] +1 for the original suggestion. +2 for Kris' newtype-only suggestion -- especially if we can actually prevent orphan instances effectively. (I think I got that right, it's a big thread at this point.). IMO, it's fine to force people to at least *consider* which instance they want absent a "best" answer. I do think it's important that we are actually able to effectively prevent people from just declaring orphans willy-nilly. +0 for _hvr's dual-incompatible releases. It would be a +1, but my worry here is (as usual) the worry about *forcing* the whole ecosystem to upgrade all at once. Usually this is not actually a big deal, but "containers" is used by almost *everything*, so it's effectively a "split" until everything upgrades. (Obviously, things are not quite are dramatic as that since, presumably, relatively few packages actually use the instance in question, but...) Cheers,