Since it's purely theoretical I voted Kodan. I'd like to see them as a playable race, but other than them probably Tengu. Dwarves would be also very cool but they're all underground and the have their story in GW and besides techical reasons they would require sotry/lore overhaul to make them playable. And from the lesser races Skritt, Hylek, Quaggan or Grawls would be interesting.