http://u.qdnx.org/file/bobjonkman-20150124T221102-w7jm588.html
I think federated group takeovers are unlikely to happen. It could happen in today's non-federated groups too, but all #Fedizens seem to be a polite bunch. And if a takeover of a federated group gets to be too much for an admin, she can always remove her server from that group, and start another group.