There are 2 main foes to be slain:
- The Burning Legion (Kil'Jaeden and MAYBE Sargeras)
- N'zoth
A Burning Legion expansion should explore the twisting nether and other demon infested worlds, such as argus, Xoroth. An Old God expansion should explore the underwater schemes of the Naga, and the emerald nightmare corruption by Xavius. Personally, I would love more this old god expansion, but it everything points at a burning legion expansion.
Edit:
People fail to see that we still have one more year in MoP expansion, will have 2 years of 95 expansion, and 2 or more years of 100 expansion, it's more than 5 years. Do you think wow will last after 6 years, with more and better games releasing, including the Titan Project? So yeah, I would be a lvl 100 cap.