Two words, Sub-Races.
This would mean simple reskins, but truly, what would the difference be?
Well for one, they could have instanced starting areas, clearly a Taunka wouldn't start in mulgore, a dark iron would probably start in Searing Gorge too. This would provide greater variety with much less effort and consumed resources. It would satisfy your roleplayer, it would satisfy your raider, it'd satisfy your lore junky too.
This would open up a door for ideas people are -begging- for. Like High Elves. Though that might be pushing it, High Elves as a sub-race for the Night Elves, carrying a similar skeleton, but with a high elf skin, and simple high elf edits to the model so it isn't a parallel to the blood elf.
What would this mean for racial abilities?
GC said himself, that if he could he would have made WoW without racial abilities, where your character was your character, not played for the races stats or racial abilities. This would be the perfect oppertunity to drop the racial ability jazz. And instead, perhaps, give each race its own unique aesthetic abilities, like in Guild Wars 2. [I think?]
In my opinion, sub races have little drawbacks, But lets hear it from the crowd, what do you think?