I'm fairly certain that this is a tactic for dividing the mass of players between 2 areas rather than funneling them all through the same quests. The paths converge eventually (probably pretty early) after what I suppose seems like a decent enough period of time for players to be somewhat spread out. I expect it will be a lot like when you pick a starting city in that you can't go back and do the other set of quests with the same character, but it's possible that it will be more of a do A or B first, then do the other scenario. I don't think we've had clarification on that exactly.