On another note, I read this... possible expansion story lines?

"The Burning Legion is small potatoes in the grand scheme of things. We took out their de facto leaders twice within this generation of mortals. It isn't they aren't a threat, but their big muscle was always Sargeras who is MIA for different reasons depending on the most recent retcon.
The Burning Legion itself is a big threat, but it is Deathwing or lower without ol' Sargie making a return.
Now, with MoP we even see that the threat level doesn't always escalate. What is at least on expansion level threat league, but doesn't need to be Deathwing/BL high? The Titans, the Old Gods, and maybe Azshara.
The Titans are a possible expansion villain in my eyes. Not Sargie, but the Pantheon. Remember that the Deathwing story arc began in Vanilla and was touched upon every expansion since them (some more so than others) and has been passed to Wrathion.
The Titans are similar. We have the recovery of the data disks in Uldaman in Vanilla. In Wrath we had Ulduar and the Algalon storyline where he decides to spare us, but we have to send the message. Meaning the metaphorical envelop saying "all is fine" has the address written handwriting that the Titans may be able to read, but recognize as not Algalon's. In Cata we destroy the weapon Algalon was meant to use (Halls of Origination). If they had an alarm set to go off if Loken died don't tell me that didn't send a second alarm. One that would raise eyebrows considering it happened so soon after the "all is okay" message was sent. The whole Mogu storyline is Titan laced, and potentially more alarms being sent with these ancient machines (including holding cell for Ya'shaarj) being messed with.
Mark my words. The Titans are coming to find out what the hell is going on with Azeroth.
The Old Gods could be three expansions on their own since Blizz has hinted they have a similar goal, but aren't all in lock step. It wouldn't necessarily being OMG Old Gods all the time similar to Cata, but a background plot similar to the Sha of MoP.
There still is N'zoth who was as Ghostcrawler put it "writing Deathwing's checks". Cata set him back, but we didn't take out the boss. Cata was the equivalent of purging Northrend of Kel'Thuzard, Anub'arak, and a few others, but never taking down Ice Crown Citadel. Instead Neo Naxxaramas, or something, was final instance with the power to take the fight to Kalimdor and Eastern Kingdoms. Don't write this guy off.
There is also the Old God responsible for the Emerald Nightmare. This has mostly been seen in the non-game materials and wrapped up there. However, it would be easy for Blizzard to bring this back since they left some wiggle room behind.
There are five old gods. C'thun is dead, but is trying to be rezzed by his followers. Yoggiekins of Ulduar is effectively dead. Y'shaaraj is out as of this expansion. Remove N'zoth and Emerald Nightmare we have a fifth one yet. Either we know nothing of this guy/gal/thing or it is the one bank rolling Azshara.
Azshara is interesting. She has lots of Ifs with her being an expansion villain. She could be to the Fifth Old God what Garrosh is kind of is to Ya'shaaraj. She could play in with Sargeras and the Burning Legion. Keep in mind she has Neptulon kidnapped and presumably under her mind control. If she has split from the Old Gods she still has managed to take control a portion of one of their forces. I'd say the only thing really holding her back from the role is bad memories of Vash'jir and how to work an expansion where the main threat is under water.
Sargeras I'm kind of leaving out as I have trouble seeing what he could be alone. If he isn't making a presence with the Burning Legion it would mean his eventual showing would be Burning Crusade 3.0. It is possible that he might end up showing in the Titan Expansion that I believe is coming. The Titans come not as antagonists, but figure if we have defied the odds so far that maybe we can help them against Sargeras? On the other hand, if Sargeras is in the upcoming Burning Crusade 2.0 expansion that would give the Titans another reasons to get off their couches and see WTF is going on with Azeroth. If we can repeal Sargeras 2-3 times (War of Ancients, Medivh's Mother [somewhat], BC 2.0) we may be an even bigger threat.
That's six possible expansions right there without even resorting to left field ideas like Mists of Pandaria. There is even a possibility of using retaking Argus (Draenei home world) as to MoP what this Burning Legion expansion would be to Burning Crusade.
EDIT: One last thing about the Titans I feel many forget. They loved nature. But the sentients they made? All golems and machines. Our fleshy little heroes will look as tainted to some of the Titans by the Old Gods as the Faceless Ones look to us. The Titans aren't "Good", but Order. Maybe they will be chill in the same way the N'aaru are with Light/Shadow with us being in the middle. Then again, they could be Knight Templarish considering they are the opposite of the Old Gods (for the most part) while the N'aaru are Light and Void within one being already."