So on the Blizzcon schedule if you read the blurb for the Warcraft Panel: "
The invasion was just the beginning. Join the World of Warcraft development team for an in-depth look at what’s in store next for Legion players."
Just the beginning huh? So we bring the fight to the Legion for once?
Also this deleted leak video which shows what will happen in Nighthold:
https://www.youtube.com/watch?v=1XmP0ZGTWXI
At the end Illidan says:
"...Follow me into the Abyss!"
So yeah calling it now: After Karazhan we enter Argus or some world in the Twisting Nether and/or The Void.