First, i'll say that these are just rumors and not 100% confirmed facts. Supposedly...
Profession Boosts - They're going to start selling profession boost from 1 to maximum level. Yes, this even includes Fishing and Archaeology.
Pets/Mounts - It's not enough that there's optional pets and mounts in the game, but they're toying with the idea of selling rare mounts like the mount from Tempest Keep and the Karazhan mount on the Blizzard store as well.
Extra Gear Rolls - No, i'm not even joking. It's been rumored that in WoD they're thinking about letting people buy extra roll chances on gear if their bonus roll should fail to award them gear.
There are more paid feature ideas in development as well.
I'd like to hear your thoughts on these rumors.
Part of me thinks they wouldn't be low enough to start selling all of this crap but then part of me thinks that they just don't care anymore and they're going to trying to milk as much cash as possible while the game's still popular.