According to an interview Ion did, layering will be by continent rather than zone, so there will be multiple copies of high level zones on the same server if the overall population warrants it. It’ll be gone either when the initial population spike dies down a bit, or when phase two (which includes Kazzak and Azuregos) launches. It does seem like there will be ways to exploit that for quests, rare spawns, nodes, etc but I guess we’ll see.