They should make a world pass system again, when a server starts to fill up, lock it unless people have a world pass from someone already on that world.

People should just be patient though, the servers will open and close a lot within the first few days/weeks to try and balance them out, so don't panic if your chosen world is unavailable, just wait a little while. Also the 6 month limit for 1.0 player transfers if probably just to non-legacy worlds, I don't see any reason why they would prevent you from transferring from one legacy world to another.