One of the bigger reasons uldah is overpopulated is the fact that it's the best designed city and with that everyone wants to be able to communicate for events easier. If there was a world chat channel for events it might alleviate the stress being put on the city and spread people out. A channel for each event like dungeons, primals, behests, leves, hamlets, etc. What might prevent the spreading is simply due to the way uldah is designed. Everything is closer together, more compact than the other cities so doing this might not change anything. If it was added, being required to do quests and them being "linkpearls" or something of the sort would probably keep to the game.