Well said, Lucian.
There's a reason that players have all congregated in one city. It's because it makes the game more enjoyable for the players. It's a way that players have minimized many of the game's problems. If we didn't like being in one place, we wouldn't have all moved to the same place.
1) No Means of Travel. As Lucian said, the regeneration rate for anima is already painfully slow, compared to the amount of anima players use daily. Spreading people out throughout the world is going to make this problem worse. Players are going to be forced to spend more of their game time running -- which everyone hates -- rather than fighting, gathering, or crafting -- which are the reasons we play the game.
2) Market Wards. Buyers and sellers like having everyone in Uldah because it's one market where everyone can go. You don't need to travel to 3 different cities just to see if someone is selling one item. Having everyone in Uldah gives us the benefit of a central, worldwide market ward, even though one is not in the game currently.
So forcing everyone to divide into 3 different cities is going to hurt the economy and make it more difficult to buy and sell goods.
3) Party Diversity. Increasing class uniqueness is one of the stated goals of the new battle system. Ideally, every party would be made up of a variety of classes.
But under the new leve system, different classes are going to want to do different leves. Conj/Lnc/Arc in Gridania; Thm/Pug/Glad in Uldah; Mar in LL.
It's going to be difficult to find tanks to do leves in Grid. It's going to be difficult to find melee DPS in Uldah. And it's going to be difficult to find anyone except Mars in LL.
So parties are going to be made up of the same limited classes. That's going to discourage party diversity.
4) Social Aspects. Currently, one of the biggest benefits to having everyone in one city is that there are usually people on to socialize and interact with. The drop in the number of active players is going to be much more noticeable if we're forced to spread out through 3 different regions.
5) No Mailboxes. There's currently no way to give someone else items unless you're standing right next to that person. Forcing us to spread throughout the world is going to make it much more difficult to give items to other players.
Someone from my LS is trying to level Leatherworking, and I've got dodo skins to spare? Sorry, man. You're in Gridania, and I'm working on Blacksmith in LL. I want to help, but not so much that I'm willing to run for a hour just to trade you some skins.
I don't mean this to be a doom and gloom post. I understand that it's going to take time to implement everything that's going to make this game whole. I'm just not sure that dividing players and spreading them out throughout the world is going to be good for anything right now (except maybe server load).