If there's no room in a server then there's no room, nothing you can do about that. What I don't want to happen is one group of friends wanting to transfer to another group of friends but since there's no room, the transferring group gets split up and sent to god knows where. Now that would be a disaster.
With this game's trend of technical issues though, I wouldn't be surprised if there were issues with this transfer either. No, I'm pretty sure there will be issues due to congested worlds and the congestion caused by the sheer amount of people who will be transferring.