@Mastodon on the comparison with XMPP, XMPP loves on as the messaging foundation for many personal, enterprise & gaming platforms. Early on, companies like Antepo were bought & folded into commercial enterprises, Adobe messaging service in their case. A variant of XMPP lives in Zoom. The real question is, long term will ActivityPub interoperability have a viable business case or will the protocol & server implementations power smaller, isolated branded experiences?