joe, Remember the world around 2007, where you used @pidgin so that you could be logged into AIM to talk to your US friends, ICQ for your European friends, and YIM and MSN to talk to those 3 weirdos all at the same time? Eventually, folks like AOL and GTalk added XMPP support. #XMPP let you "#Federate" between services but the promise of XMPP never really became a reality (example: https://superuser.com/questions/717272/is-it-possible-to-talk-to-aim-users-with-any-jabber-client-via-any-jabber-accoun).
I have hope that #ActivityPub does what it couldn't. You can already follow #PIxelfed, etc.