Seems like RCS and Jabber have interesting things to say about federation/superpeering, namely that if it's too hard you end up with a centralized system. People trying to use Radio have a hard enough time understanding what the community server does versus what their own copies of Radio do, much less that the community server isn't the community server but rather a community server.
Jabber seemed to have this problem as well. The Jabber folk encouraged people to run their own servers to make an interserver network, but everyone got accounts on jabber.org and jabber.com anyway. These days that's less so, but I'm not hooked into the Jabber community anymore so I don't know to what extent, or why. Maybe it's because Jabber is so technical a thing that the people into Jabber do understand that "the" servers are only "those" servers.
Superpeers have to be literally super peers, normal peer nodes that happen to be better connected. I guess that's the difference between "superpeers" and "federation:" federation is hard, and the superpeers are qualitatively different, whereas real superpeers are the same, only operating at a different scale.
(I confess I'm no rigorous scholar of P2P or distributed anything. This would be interesting with respect to TypePad or Cornerhost Rantelope, but those aren't even federated—especially not TypePad, as Movable Type's license forbids federation, though not by name.)
