I finished the Elisande encounter.. in raid finder today.. and throughout the nighthold you are racing agianst time to stop Gul'dan from using the nightwell to summon his master Kil'jaeden into the world of Azeroth.
The Tomb of Sargeras Audio does mention or hint at this incredible power source he could possibly use for himself, but after listening ot it all, I'm safe to conclude that he's fallen in line with the legion and now seeks to bring his master into Azeroth to finish the job they started in the War of the Ancients.
I've done it on raid finder too and I've never heard of anything about Kil'jaeden. It's Sargeras. Even the dungeon journal abilities show that. It says phase 3 he beseeches the power from his master. Then he proceeds to get abilities like Flames of Sargeras and Storm of the Destroyer (one of Sargeras titles).
Also Gul'dan wants to put Sargeras soul into Illidans body:
https://youtu.be/fcdYHU9hS0A?t=274
It said in the Chronicles that he sent his avatar intending to kill Aegywnn
“He unleashed his terrible might on Aegwynn, intending to destroy the Guardian who had thwarted his agents for so long.”
Excerpt From: Blizzard Entertainment. “World of Warcraft: Chronicle Volume 1.” iBooks. https://itun.es/us/ee4sab.l"
you could be right there actually, i just assumed his "master" was referring to Kil'jaeden as according to Tomb of Sargeras this is who Gul'dan's master is. Kil'jaeden's master is Sargeras.
He may be talking about the infusion of Illidan's body with Sargeras' - or Kil'jaeden's entry or both.
So how many people know that Sargeras is still out there? Or is he dormant while Kil'Jaeden rules the throne...?
I know we do, but the citizens of Azeroth don't have access to wowpedia.