It seems like Blizzard is setting up Anduin to be an anchor between the horde and the Alliance and it would be very interesting if the horde were to pledge their allegiance to Anduin in the next expansion as the supreme leader of Azeroth.
If in fact there was some faction allegiance system where horde and alliance players could do some quest event or reputation grind to become "neutral" or friendly with eachother's faction, could it make sense to have a well liked leader from a faction become the leader of Azeroth at least temporarily?
Keep in mind this is just a question to horde players. I am primarily an Alliance player and the only horde leader I could see myself getting behind in terms of pledging loyalty to is maybe Thrall or Bloodhoof.