I've thought of it this way. The leader of the humans is a human. The leader of the humans is also the leader of the alliance. The leader of the orcs is an orc. The leader of the orcs is also the leader of the horde. Each race also has their individual leader. So if Voljin, Sylvanas, Baine, etc became the new leader then would they suddenly be the leader of their race + the orcs + the horde as a whole? It seems like the new leader of the horde can only be an orc unless the orcs get a new leader and they change the lore so he doesn't become WC of the horde.
Has this not occurred to anyone else as well?