It's not a case of not liking to see them before then, but whether they can feasibly drop planned PVE content for the sake of adding a new race in a matter of two and a bit months. Unless they're hiding a surprise, I would not expect them soon. It also then ceases to be a potential selling point for 6.0. I'd like for them to do it as early as 5.0, but it's just not that probable.