The first thing they really need is a new incarnation of Wintergrasp, Wintergrasp was incredible, you could jump on a steam engine and storm the fort if you were attacking or you could jump on the fort cannons and bombard the oncoming attackers if you were defending, it was possibly the coolest thing Blizzard have done to date. Blizzard tried to do a new version of Wintergrasp with Tol Barad, but it was a disaster, it failed in every way to meet Wintergrasp's level. They need something epic involving another castle or fort with something ridiculous happening to top Wintergrasp, what I want to see is two giant turtles (like the wandering isles) with giant forts on their backs and they circle each other, so its like a mix between besieging and boarding pirate ships, but thats just what I think.
Blizzard also needs to bring Thrall back as Warchief, he was awesome and gave the Horde a way of not seeming like just a bunch of evil bloodthirsty maniacs.
If they do another expansion they need to boost the level cap all the way to 100 and make sure the Titans are actually in game in person, because then they can actually start coming up with new ideas without looking like they are just milking the game for everything they can. World of Warcraft has also been in desperate need of actually involving the Titans more for a long time.
Another thing Warcraft desperately needs is house building like Runescape, it would be awesome and they could add a new gathering profession like woodcutting so the professions could provide materials for house building, house building could even be a secondary profession itself so they can be improved over time.
Rob: I was very skeptical leading up to Mists of Pandaria but Alan showed me it and it looked cool so I bought it. Since then one thing has become apparent. The charm is gone. WoW used to, for me, be the best MMO there was but now I find the formula boring. It's ok in short bursts of maybe half hour to an hour but no more than that. The quest mechanics and the combat system need a major overhaul. Maybe some real time proper combat would be cool rather than just clicking on abilities and the quests, although much better than they used to be, still seem too samey and are still plagued by fetch quests. I still like WoW but it needs to evolve or die. There are too many good MMOs out there now for anything to be sub par.
Also it desperately needs to embrace free to play. Although at the moment the subscription numbers are good they drop more and more after each expansion has been out for a while and its only a matter of time until the free to play juggernauts like The Old Republic kill it off.
Alan: These are just a few ideas that I can think up at the moment and there will always be more with a game like World of Warcraft. If you like or dislike any of these ideas or have some of your own, please comment and share your views.