User blog comment:Hawki/Demons/Reaper of Souls/@comment-199.107.213.166-20140420084717

My best guess is that post-RoS, whenever it can be, there will be one more add-on with seventh class (already planned), and after that, Diablo IV. However, if add-on would come in maybe two or three years (definitely not 2015), Diablo-IV may easily be delayed to about 5-7 years.

In the fourth game, I bet two bucks there will be seven Nephalem heroes, each possessed by one of the Evils, much like the Dark Wanderer was by Diablo. My personal guess is Demon Hunter being possessed by Mephisto. He'll have to get used to having feminine shape, like Diablo did.