Ogres should be playable, with Ethereal as neutral and changing Feralas into a Horde Zone for the Ogres, and making those ruins to the south a new dungeon as well.
It would be sweet if they changed the little to the west of Feralas into the Ogre's Starting Zone as well and make it so you can get to Feralas to level for them and meet the Horde.
Rexxar should lead the Ogres, and having Ogres with the classes that involves one-head be melee, and the spellcasters have two-heads.
These classes would be great as well for them:
Warrior, Monk, Mage. Warlock, Shaman, Priest, Hunter, and Death Knight.
All they need is, is more animations and revamps here and there, and a female model for them as well.
A perfect height for them will be Wuu the Pig Handler in Feralas and it would be sweet to have a Ogre Mage under the Horde.
Not sure what features that Ogres might have though, like a face change, tattoes and so on.
Also Mushan should be the Ogre's mount: