That's not how federation works, at least in XMPP. You only need to connect to one server that's out of censorships' reach to be able to communicate with everyone.
While it's true that my friends on other servers might be able to send messages that will arrive on my chosen server, that distinction isn't very meaningful because I am unable to connect and retrieve those messages.
I wouldn't be communicating with my friends until I switched to a new server and rebuilt my social graph.
Also, while it's not specified in XMPP (yet), it's easy to imagine a federated service that lets you connect to any server in the network that then behaves as a proxy to whatever server you have your account on.