Most people seem to find the idea of a troll a stretch, and scoff at the idea of a blood elf... a human? maybe when Xoroth freezes over.
Slaying 8bit dragons with 6 pixel long swords since 1987.
But if a human ended up being the horde warchief, there would have to be reason to suppose that the majority of the horde would support it. If the human defect were bloodthirsty, hateful of their own race, and were savages like the horde, then they may very well support him as their leader.
Putting a person in command that is more savage and bloodthirsty than them could give them the rally they need to have complete dominance over the alliance. It would be in the alliance's best interest to try to dethrone that human defect, as he would know human / alliance intel that not many horde would ever know.
I was thinking more along the lines of the leader of Si:7
I see no problem with a troll or Tauren, don't think Lor'Themar would want the title and don't think Sylvanas would either. Top 3 I can think of are then Vol'jin, Baine, or Rexxar. It'd be a damn good way to bring Rexxar back into the lore.
But human? No, never.
@Darsithis: What is your opinion on the matter of having a human be the horde warchief?
I'd have responded with just "No." but I need at least 10 characters.
Just going to pop in and say I'd recommend re-reading Lord of the Clans, since it states that Drek'Thar thinks Thrall is the strongest shaman he's ever seen, despite his novice status, so yes, Thrall is this very powerful shaman. Also he ruled over the Horde for a good period of time... roughly equivalent to Orgrim Doomhammer's time.
These two will be worse, mark my words.
http://www.wowpedia.org/Giramar_Windrunner
http://www.wowpedia.org/Galadin
Speaking of which, why didn't they re-introduce him in Mists of Pandaria with Chen and stuff? Did i miss out something as of why he was forgotten there?
OT: I don't think it will ever happen. Imagine a orc Warchief for alliance. How'd that work out?
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I believe he refers to the fact he was raised by humans.
Doubtful. Under certain conditions I could see one being a powerful advisor though.