It would be too much to have separate instances of cities for new and old players...Say Limsa sinks beneath the waves..it no longer exists...that would be interesting but if it was actually implemented i wouldnt be able to join or help out any new people that start off in the city the player population would be completely split in half and that's not a good thing whatsoever. You would only get that in a single player RPG. I can deal with the shifting of NPC's but for a whole city to be left ruined (say limsa sinking or even Mor Dhona being attacked by the Garleans or some such) i think is a bit much for an mmo where there are thousands of individual players connected to one another on a single server.