It's not (yet) dead! We even will have #Jabber #XMPP hack night today:
https://mov.im/?node/pubsub.movim.eu/berlin-xmpp-meetup/ab62371c-c50f-43b0-826e-7d7027f64750
All federated protocols suffer from fragmentation issues. Even email. E.g. my mail client doesn't support HTML emails, Other clients do not OpenPGP.
XMPP has at least feature discovery ("disco"), e.g. my client can see, if your client does support A/V call. If not, it won't show the phone receiver symbol.
(Tonight I will hack on either #sms4you or on #libervia Debian packaging.)