We've all cheated on WoW before. Whether it was Warhammer or Free Realms, we've all come back to the game. While Blizzard does a lot of things right, once in awhile, we play another game, see something cool, and ask ourselves, "Why doesn't Blizz do that?"
We've all seen talk about an appearance tab, where players can, for example, wear their Christmas clothing for looks while actually having the stats of their raid gear -- the only real difference is the looks. Rift recently announced this feature, so with any luck, much like with guild quests/challenges, the Blizz team will feel like borrowing this as well.
Housing's another idea that gets tossed around. It was actually being worked on in alpha, but Blizz decided not to go with it. In other games like EverQuest 2, player housing is also what makes towns. Why not allow players to use some space in capital cities and outposts to house their guilds?
In a similar vein, I'd love to see some world PVP that can be captured only by guilds. Darkfall's player housing is linked with a conquest system in which players get to keep their houses but the conquering guild gets some cash for their guild bank and their name in lights. Every, say, six hours, a town gets "hot." Imagine if guilds could "capture" Crossroads and have their guild advertised as its protector or take over a rival guild's home town to start some world PVP guild wars?
What features from other games would you like to see in WoW? Player-owned ships? Terraforming? Factionless PVP servers?