I have always thought D3 was going to be battling the heavens. Only because the three prim evils were defeated. I know they show a Diablo looking character in the trailer. I think if they brought back Diablo and the other primes, It would be to fight over the humans rather than fight the humans. So basically Alien vs. Predator scenario. Kind of a choose a side thing. Only that I think our main Characters will be on the Human side and fight both of them.