Far more likely than any of these, is that Imperius will descend to the burning hells for revenge, and become the new Prime Evil of Wrath, as hinted in the cinematic, and in the game. He's becoming more and more irrational and bloodthirsty, and the Wrath short shows that his short temper is in part something Diablo desired.
He blames humanity for what happened to the heavens with Diablo, and wants to wipe them out. He also wants to destroy the burning hells. Its not unlikely he may make use of the black soulstone to do so.