I’m all for Draenei Demon Hunters, as long as they’re Broken. 
But stuff like Draenei or Mag’har Warlocks? Both of them would cease to become members of their culture as becoming a Warlock would betray a foundational element of their culture.
On the other hand, I am open to certain things being expanded. Eredar Warlocks? Yes, please! Adding the Hellfire Fel-black Orc skin to Mag’har that automatically applies when they choose Warlock? Hell yes! Tossing in Highmountain Warlocks because the developers forgot about the Feltotem when assembling the class list? Of course!
Hell, Tauren Paladins are one of those things that would have put me off, but they did a solid job expanding the scope of what a “paladin” means in the context of Tauren culture.
Honestly, as long as they go further than “Well, X race taught X race,” with their lore justifications, there is potential for any combination to work. But they do need to put in that effort where it’s required. It needs to feel like a natural extension.