Now it seems that we are going to overlook them as a whole.

They have been a major part of every expansion set on Azeroth. Vanilla - C'thun and his Qiraji. Wrath - Yogg and the Nerubians. Cata - N'zoth's influence on Deathwing and the N'raqi/Faceless ones. Mists - Yshaarj and the Mantid. Legion - Various influences/Il'gynoth/Setup for BFA. BFA - G'huun. Azshara. N'zoth.

Outside of the expansions set on Draenor, every expansion has had major dungeon and raid bosses related to the Old Gods. Mists and BFA were basically given over to them entirely. We've fought the Old Gods themselves, their servants, their corruption. We've explored their respective aqir servant races and fought them seemingly endlessly as dungeon bosses. We've cleared out more Titan facilities dedicated to Old God suppression than I care to remember.

Short of a full Black Empire comeback (which I think is beyond the scope of what would functionally work in-game) I don't know what else you could even do with them.