Are direct messages the same sort of thing, mechanically speaking, as a status update in activitypub/Mastodon?
Is it possible in principle (api extension?) to make a DM that can be boosted?
Imagining a bot that boosts every message to it. You now have a Mastodon-based chat room. Messages don't appear on your timeline, only to people who follow the chat. You could put the chat in a column, you could create an external site with a "chatroom-like" interface which is skinning underlying Mastodon.