I have a feeling we wont see rubraces this expansion, but maybe next one. They would need to tweak the starting zones slightly, after all. Like, to explain why Mag'Har orcs are in Durotar, and doesn't the opening cutscene for dwarves explain that you're an Ironforge Dwarf? The easiest graphical subrace, Gilnean Human, would be awesome to play as, but the entire starting zone is about you becoming a Worgen. They would need separate starting quests.