Even if bloodthirsters and bloodletters are already in the game, I dont think we will get a Khorne sequel for the simple reason that the XCOMesque gameplay of Chaos Gate doesn't jive well with an almost exclusively melee enemy. Kiting them would be way too efficient, same with overwatch and area attacks in bottlenecks. They would either have to nerf a bunch of stuff or take it out of the game entirely which would make it unrecognizable.

Slaanesh is impossible to do PG enough without seriously cutting back on the whole aesthetic and suffers from some of the same limitations Khorne does, so I think we can forget about that too.

That really only leaves 3 options:

Undivided/Be'lakor, Tzeentch and Vashtorr/Dark Mechanicum.

I'm praying for a bigger game with a Chaos undivided faction as the antagonist. I REALLY want to smack around Word Bearers and Lorgar. What do you think?