Yeah, I've know of this for a while now but I stayed away from the topic for now, mainly because I was convinced during Mists of Pandaria that the next expansion was going to be "the Dark Below" and when they presented us with Warlords of Draenor I just remember thinking, "well that is stupid." And yeah, the Dark Below ended up being a myth... Instead they pulled out Warlords of Draenor to promote the WarCraft movie.
But if I were to use logic, we see a new leveling gear-set which is named after Kul'Tiras and it contains a map with strange looking tentacles on it. Combine this with a quote from Xal'atath, "The God of the Deep writhes in his prison, breaking free ever so slowly. You should hurry and defeat the fallen Titan... there are greater battles yet to fight." It seems like Blizzard is hinting towards an Old God expansion and Kul'Tiras will play at least a part in the story. A few things strange about this, if N'Zoth is truly a underwater why are we going to Kul'Tiras as the island lies between Kalimdor and Eastern Kingdoms. Why is this strange? Well if N'Zoth was locked under the water then wouldn't he have to be East of the Eastern Kingdoms? N'Zoth was jailed prior to the continents seperating so logic dictates that if he was really locked underwater it can't be found near Kul'Tiras, so why not use the Teldrassil harbor instead?
Second thing I'd like to ask is what is Jaina doing in Kul'Tiras, she hasn't been there since she helped kill her father. Why would the people of Kul'Tiras ever want to have her rule them and even prior to killing her father she spent very little time on the island, why she'd consider it a home is beyond me.
But there's one thing that has me believing this will be a Void expansion and that is this:
That is Alleria Windrunner corrupted by the Void, seems as if the Void Lords are more present than you may have thought. Also what if I told you that we have proof that Sargeras is only a puppet, doubt me? I wcan't blame you but for you to understand you must know the story of the "key to all worlds" as Illidan calls it. More well known as the Sargerite keystone this artifact can open a portal to any other world like Azeroth and that's just what Illidan uses it for. But stop to think about how strange that is, the grand goal of Sargeras is to destroy Azeroth right? So why then is it that he has known the location of Azeroth for at least 10,000 years yet never used to keystone to transport himself and/or his entire army directly to Azeroth, he has the power to do so?
So we know for a fact that Sargeras says that his goal is to destroy Azeroth and he has always had the power to do so, then why hasn't he? To find that out the logical conclusion would be that he works to further the goal of whomever this helps out. After all Kil'Jaeden told Sargeras "All we have done has been by your design yet all we have to show for it is failure." So Sargeras can clearly not be working for the benefit of his own organization, the Legion so who does he. I mean Sargeras is obviously not a nice guy, just look at how much chaos and destruction he has brought to Azeroth. So who would benefit from chaos, what do we know for a fact that chaos is used for? Corrupting the Titan spirit inside of Azeroth, that's literally the only one.
This is strange for me to say but the only logical explanation left for why Sargeras is making such counter-effective moves is because he's a puppet of the Old Gods. Either that or he is the most idiotic piece of garbage ever to have entered the world of WarCraft. How would you even explain away that he hasn't used the keystone, I've been trying to find another explanation since the death of Kil'Jaeden cinematic came out. What if only someone who has been on Azeroth can summon Sargeras? In that case Archimonde or Mannoroth could have done it. What if only those not corrupted by the fel can summon some outside of the Twisting Nether? There's no mortal alive more touched by the fel than Illidan and even if we ignore that he could just have sent over the keystone to queen Azshara and she could have summoned Sargeras. Sargeras has already proven that he trusts others with the keystone and quite literally no mortal has ever been as loyal to Sargeras as Azshara it's a no brainier.
So either A) Sargeras is the supreme idiot among idiots, or B) He is a puppet of the Void Lords.
Even patch 7.3 supports this not only Alleria but several other models are void based. This is why I believe that N'Zoth will be the next boss because Sargeras all has to be a part of its plan for Legion to make any sense, the masters of N'Zoth, the void lords must have controlled Sargeras. Because right now it is canon that Sargeras for at least the past 10,000 years had the power to destroy Azeroth yet never did. So it makes sense that the next expansion will focus on N'Zoth and it will serve as a gateway towards the true enemies, the Void Lords, who will be the final threat of WarCraft.