I guess from a story perspective it could seem interesting..
BUT there are loads of reasons why it would be ridiculous within the wow setting.
First and foremost, the Human leader, being a breakaway from the Ali, I don't think any Horde would ever trust that he would have their own best interests at heart. The horde would entirely become some human guys tool for revenge against the Alliance? I don't think that would sit well with them.
To be GENUINE in his leadership of the Horde, he'd have to legitamately believe that the Horde are superior, the Ali should be crushed.. which takes a really crazy amount of self loathing and inferiority issues, and bias against an ENTIRE race, that I don't think would appeal to the Horde much either.