I won't lie: I cheat on World of Warcraft. It happens, but she's a forgiving game. She keeps my friends in largely the same place while I'm gone and sometimes lets me introduce new ideas from other games to her. Usually they're features, such as XP from battlegrounds or guild quests, but sometimes other skills too, like gemcrafting. Blizzard has even previously mentioned borrowing skill mechanics from other games. I'd love to see more skills added for the next expansion!
Woodworking's come up a few times, but perhaps it's too similar to things we already have. Dual-wield pistols came up as well, but for some reason aren't coming quite yet. However, what about animal husbandry? You could potentially breed new companion pets, mounts, or even hunter pets! Or maybe add in a whip skill, allowing people who choose to give up their ranged slot for a bit for to use a consumable whip that works similar to Death Grip, Root, or even a taunt or silence, depending on the variant.
What kind of skills would you like to see added to WoW? Masonry for house construction? Zeppelin licenses to pilot large, multiplayer airships? Bug catching as a fishing/archaeology hybrid?