It would solve so many problems from XI:
1)Overcrowding- people in an overcrowded server would be able to easily log out if they choose to do so and join another server.
2)Never seeing a friend in a different server- If you and a friend own the game you might never see them cause they're in a different server.
3)Lack of gameplay diversity- with different amounts of people in servers you can one day play a server with a few people on a soloing mission, and the next play in a large party on a crowded server.
It's ridiculous that in XI you needed to pay money to switch your server. Such an incredible waste of money. Most any other mmo you look at today will have server choosing at login, why shouldn't this? I hope SE adds this feature.