@jonkulp XMPP is more than federated IM as we think of IM. More like federated message passing. Might as well be between things (buzzword: #IoT) or people or you use it to negotiate realtime audio/video communication.
And it is more reliable (though more bound to authentication) than SMTP, which means that even for IM it fills a space in federated internet communication that e-mail doesn't cover.