If that whole concept of certain allied races being folded into customization options for their parent races actually comes true, then I think a lot of those old Horde-aligned races have a fairly strong chance of finally getting added in. It'd be fantastic to finally have forest trolls as well as the Yaungol and Taunka. Alliance seems pretty light on that backlog though, as all that immediately springs to mind are the Wildhammer.
Hopefully Ogres will finally happen one day too. Don't really care either way for the Mok'nathol, but it'd be cool to just see them around more often like the Hozen.
Ogre's are the truly crazy ones. Stonemaul, Dunemaul, Dreadmaul and now the Iron Horde ogres, it' s overdue that they get added as a playable. The "too big" argument really doesn't fly either ,since Tauren, KT and Zandalari are all scaled down already.
Eh, it's pretty subjective. I think bisons look pretty awesome IRL aswell, so I naturally like the Taunka's smudged face. I get that most people prefer the normal face, though.