Still got lots of lore left.

1) 5 old gods, 2 killed (C'thun and Yogg Saron), 3 left, N'zoth and Y'shaarj, 1 yet to be named
- Y'shaarj might make an appearance in Mists, seeing as it's responsible for the 7 Sha (Anger, Despair, Doubt, Fear, Hatred, Violence, 1 yet to be named)
- N'zoth will most likely appear in an Emerald Dream themed expansion, alongside with the naga city of Nazjatar

2) Eredar, Kiljaeden and Sargeras and a host of others

3) Titans, the pantheon

We didn't kill him, we merely banished him.

Yeah, but involves more cost and development time. So...