Why centralization? XMPP users are identified with their JID in format username@server.example, similar to email addresses. And server to server communication i

Why centralization? XMPP users are identified with their JID in format username@server.example, similar to email addresses. And server to server communication is very well documented and major XMPP servers for instant messaging (ejabberd and prosody) both allow server to server message exchange. I don't see any benefits for Matrix when it comes to federation and I wouldn't agree with you that by using XMPP you tolerare centralisation at all. It's level of centralisation is comparable to that of email (and email is very well federated in my opinion). MUCs like the XEP you mentioned are handled by a different XEP.