@0 yep. And XMPP has had in-band registration for quite a long time, I think. They simply ignored a lot of working ideas, XMPP pubsub and Frendica/Hubzilla seemingly the major sources.

Creating an XMPP account on a #Libervia or #Movim service doesn't seem a bad idea. Libervia lead @Goffi is even bringing in ActivityPub interoperability to Libervia.