The game is not designed to support a population of 12,000. Much less go higher than that. By this, I am referring to the amount of lag in Dalaran (fps and latency), difficult competition for ore, herbs, quest mobs, etc. The list goes on. The systems of the game break down when there are this many people. Allowing more than what there already are is not an option. This is not something that can be "fixed" without redesigning many core components of the game, and doing so would make the game be something other than WoW.