I think this draft is OK, if people feel like it, though I'd prefer the "ranked" sentence to be removed or clarified.

I reviewed the diff since my last dnsdir review and also some further discussions about this draft.  While the draft does add some annoying edge cases (if one wants to implement this properly) and I'm not fond of some additional complexity around fallbacks and tracking which servers support this, it seems perfectly OK to leave these issues to vendors to deal how they see fit.  The draft allows for selectively replying without multi-qtypes, so that can also be used as an escape hatch (though it will increase the round-trips needed).