WebRTC is a better reason to be ringing the Skype-is-now-a-commodity bell.
Facebook seems like the only company that can bring a real network of users to something like this. Google has GMail, but they haven't been able to translate it into any type of social experience at scale.
But their strategy would indicate that they wouldn't implement federation. They would create their own closed system. Facebook is all about growing the value of their social graph, but with very limited interconnection or federation.