Was discussing this with my fiancé a couple hours ago... So far the old gods we have seen are C'thun (Original WoW), Yogg-Saron (WotLK) and the remains of Y'shaaraj (Pandaria).
Notice something with the expansions? Every one of them it's an odd numbered expansion.
Also, in Legion we will visit the Nightmare (That N'zoth is corrupting and it's implied he's in the Rift of Alm, the deepest zone in the emerald dream) as a raid , Azshara herself (Who was transformed into a Naga by him) it's involved in some quests looking for the Pillars and in the pre-expansion chain when we get to Ulduar, Faceless ones (Old gods soldiers).
Someone called Phlynch brought to my attention that:
Not sure what else everyone thinks. Just my two cents.There are three main things that lead to old god death:
- Odd numbered expansions
- Titan themed areas
- Bigger villains as the advertised threats
Legion is an odd numbered expansion set in an area full of titan themed stuff where the advertised threat is the largest demon invasion in history.