My main thought with regards to "are fediverse DMs at all secure" was that the kind of people who seem to be interested in building IM clients always seem to be super into making it secure, and thus would probably prefer to go off and make a client for a more secure federated protocol, or make their own protocol because surely what the world needs is a 47th IM protocol that makes a slightly different set of choices than the preceding 46 that nobody's using. :ds_wink:
Getting all chat, public or private, on the same publicly-owned protocol is not a bad aim in and of itself. I just feel like "omg NO PRIVACY" is a thing everyone who makes these types of clients is going to be screaming about.