Dark Iron dwarves have literally been playable since Cataclysm, yeah. Blizzard added a bunch of ashen skin tones to dwarves in that expansion to facilitate their joining the Council of Three Hammers. Heck, lore-wise, when you play a dwarf mage or warlock, you're straight up playing a Dark Iron dwarf. I always thought it was rather odd that Blizzard forgot about all this when the idea of Dark Irons being an allied race was going around. Then again, it's more likely that they simply didn't care.