I'm already self-hosting a XMPP and a Matrix server, just in case. A shame that most of the group chats I've found there are about free software, assorted geekery, but not much of what I'd usually find on Discord - hopefully that changes in a few years.

Unlikely. They make for poor discord community replacements. There’s just too much complexity at the door.

Most things are looking towards fluxer as the replacement. Since it’s actually a discord replacement unlike xmpp or matrix. Which are alternatives not replacements.