In the example of chat, XMPP is federated, it even has serverless messaging ( https://xmpp.org/extensions/xep-0174.html https://xmpp.org/extensions/xep-0174.htm

In the example of chat, XMPP is federated, it even has serverless messaging ( https://xmpp.org/extensions/xep-0174.html https://xmpp.org/extensions/xep-0174.html ) SIP for instance is perfectly happy to do ip<->ip calls (well ignoring NAT issues - one day we will all have ipv6 addresses....) This really is a solved problem, people for various reasons have decided to rely on external services they have no control over. I don't think we need to throw yet another protocol at the problem, instead we should focus on making what we have better and easier to setup and use.