So, while running some old raids earlier. Something that kinda stuck me was Illidan during the final fight of Mythic Nighthold. When beating Gul’dan and Illidan’s Demon Within appears, it is covered in Purple (void colored) Markings, instead of the Green Markings he had when unleashing the Demon Within during The Black Temple.
Also the line of dialogue “Behold the shadow of what is to come, the endless darkness that shall consume your World.” doesn’t exactly sound like Sargares’ intent.
He also stays behind, presumably to fight or guard Sargaras. But we know the void also has an interest in the Seat of the Pantheon, due to the dialogue spoken by Knife Xal’atath when arriving there “Long have we sought entry into this realm! To think we have a mortal to thank for giving us our foothold. Your service will be remembered!”
So what exactly was that Foothold? Just knowing the Location or the fact that we left Illidan behind, maybe?
Edit: It also made me think that the expansion “The Last Titan” may refer to some singular Titanic Survivor, if the Void attacks the Seat itself.