DM's seem to be waiting for White Noise to really work well, and I wouldn't expect anything before that. That said, it does sound like something that is, indeed, coming, and frankly promises to be the best damn DM's out there, given that it'll basically be Signal but without the need for a phone number.

Until then, we almost have too much support for DM's, because people try to use them despite the fact that they're a dysfunctional mess. Maybe throw a profile field for an xmpp address and call it a day.