The 'hub' of a game such as this will always change to where the most 'action' will be. In 1.0 the hub was Ul'dah, 2.0 it started in Ul'dah then migrated to Mor Dhona. Now it's... well, wherever it is. Next expansion it could well find it's way back to Mor Dhona or Ul'dah. Who knows. Either way, it's going to be where the players are, which is entirely out of Square's hands.