I doubt it will be likely to come soon, as it would require two worlds to be running on the same server at the same time. This would mean that there would be an extreme FPS drop.
So I don't think that this will be implemented anytime soon.
Rollback Post to RevisionRollBack
Don't feed the troll dude. And if you do, make sure it's some cheddar with rat poison in it.
He will implement them probably when he begins looking into server to server travel. As is, you can run a server that is strictly nether, but it will be some time before we see it implemented as it is in SSP.
It's been almost three months since the Halloween Update and nothing has come of it. How much longer will we have to wait?
The Universe is cool enough without making up crap about it - Phil Plait
So I don't think that this will be implemented anytime soon.