I heard it on good authority that the main bad guys in the next expansion will be ...
...
...
...
wait for it wait for it wait for it wait for it
the VIRMIN! The plot is basically that some misguided visitor to Pandaria brings back a couple of virmin to Eastern Kingdoms, whereupon, without their natural Pandarian predators, they breed like crazy and upset the entire ecosystem. The three farms that have to feed the entire city of Stormwind are soon overrun and starvation looms!
The expansion will be called "World of Warcraft: Curse of the Turnip".
Some other details in case you are wondering: the level cap will be back to 60 as it was in Vanilla; higher level characters will earn negative experience for quests and killing until they are back down to 60. Also, the raid system will be merged with the pet battle system, so look forward to 25-man pet battles!