A Server Federation would nice, because it could help to keep this game attractive for some years. Since most worlds have an unique salt this could be seen as an Adress which could be entered into an Portal (just like in Stargate). If one finds his Portal and an Adress, they could try to enter another World, to do what ever they want.
The technical idea is inspired by the chat protocol http://de.wikipedia.org/wiki/XMPP where a user connects to its Server and when this user wants to talk to someone on another server the servers do all the transport of informations.
To Implement this you would need an Masterserver which would translate the salt adress to the ip/port. Therefore you would need an protocol which would allow the Server to stream the userdata to other servers as well as an enctrypted database to prevent cheating. There will also be some other problem like script restriction to allow owners to develop and share new technology but to disable god mode scripts etc...
It should be possible to disable the encryption to keep the current support for modifications, but to enter the Federation the Server needs to be encrypted and somehow validated since the first start.
I guess you understand the idea, because there are a lot of movies that do the same but i don't know any games that would support such a feature. Distributed Services is nothing new in the context of web appliction but it would be new for games with dedicated servers. Well yeah and the new World of Sandbox Survival Games would be just be perfect to implement this idea.