Pixelfed is also adding something like that, and Pleroma also had it for a long time. But personally I think it is a bad idea to re-invent the wheel badly on protocols that were not designed for chat.
It is not very difficult to link a fediverse instance to a XMPP server and get proper high performance and e2e encrypted secure chat with it.
Fair enough. Still, given that each platform seems to have some DM/chat interface that is probably misleading to most users in how much it isn’t really that at all … having something more chat like might be better than nothing … unless it’s just removed?