Well, number of remaining races grows thin as expansions go out, but I just got struck by sudden idea.
Because in 7.3 we will most likely get in touch and close cooperation with the Army of the Light...remember, they actually are remnants of races decimated by Legion. So, after the war on Argus ends, where would they go? Their homeworlds are shattered and/or fel-infested, they can't live there. Traveling through the Nether...well that's not too good.
So why won't the refugees from the Army join Azeroth, just like Draenei did?
Aldrachi - an Alliance race, for example. Yes, completely new and fresh.
What for Horde, have no idea, really.
But I'd like to see an ancient and powerful race as playable, and you?