One problem with this is groups. What would happen if you moved to a different server whilst in a group? Would you be taken out of said group?

Another thing is the balance of the game, a lot of things could get...a bit crazy if people were to do this. Plunder and such could become harder or easier, it'd be much less predictable, and it could just be a lot more painful. People work towards goals, build up stuff, get titles, that could become very hard to maintain.

Another problem is that "players" are server based, "players" or "accounts", whatever you wish to call them. If you were to move to a server where you have a pre-existing character, what would become of them? And player names too, because no two players on the same server can share a name, people may be forced to change names, this really could get...messy,

The server-id nickname would work, it does make sense.

Though, rankings would probably be just in madness depending on how many people go to which server daily. People would vanish, reappear.

(Though, the biggest issue is how the game's servers are, generally separated except in a couple of events, along with friends lists, groups, etc.)