I am starting to wonder whether the decision to have 50-plot neighborhoods came from the need to make it a separate instanced zone. If it was just a handful of plots, then they probably could have put it somewhere in Durotar or Elwynn quite easily. But if they needed to make it an instanced zone, then having it be small would probably just look weird and incongrous.
Would also explain why they ahve not confirmed other neighborhoods. As I have said before, places like Bel'ameth makes perfect sense for housing given it is completely empty outside the handful of NPCs.
But if it is a completely new zone, then they need to make it from the ground up, which is probably moer effort than it's worth at this time.