We know that Warlords of Draenor takes place in an alternate version of the game world we know. And, as the trailer showed, in this world, Grommash doesn't drink the demon blood that enslaved the orcs to the Burning Legion... though it apparently doesn't stop them from being conquerors.
But now that the door to crazy alternate Warcraft universes has been open, let's make use of it! Looking back on the history of Warcraft, what would you go back and change if you could? In my case, I think I'd go back to that Nagrand quest chain where we helped convince Garrosh that he was leadership material. Why did we ever do that?! (Answer: to get the quest achievement. But it wasn't worth it!)