Asked Yoshi that question on Gamescom:
JPGames-Frederick: With the over howl of existing maps will current players be able to choose a new starting city? After changes are made, maybe a Ul’dah player wants to choose Limsa Lominsa instead, will this be possible?

Yoshida: The current player won’t be able to choose a new starting city. The reason being that current players are playing the story now and the continuation of that story with Final Fantasy XIV: A Realm Reborn – So we can’t make any changes there.
So, nope :/ I wish i could switch. Meh