Personally these are some of the things I'd like to see happen based on my own experience ...
* Make the area around the Dark Portal a sanctuary like the area you zone into when you go through the Dark Portal, I'm so fed up with going through the portal in Stormwind to get to the Dark Portal just to get past the loading screen and see i'm half dead, stunned and got no chance, this isn't fun or fair, they get no Honor points for the kill, ganking is fine, but while someone is on a loading screen?! You then have to keep ressing and being killed, each time edging closer to the portal until you get through. ridiculous.
* It's annoying when you have alts and have to grind rep repeatedly, why not make tabards account bound (add a tab on the same ui as with mounts and companions) and when you hit exalted with a faction and get there Tabard you can equip it on an alt and get their rep via Dungeons (like in Cata) or Dallies, this could also be a better way of giving the extra 50% rep bonus that the commendations give for doing dallies on alts? It would also save bank/void space and make the game more alt friendly. It could also be a nice way to see what tabards you are missing if the ones you haven't got are shown buy greyed out (like the pets)
* Add a tab along with Pets/Companions (and ideally tabards!) to show Heirloom gear, that would make it account bound, save having to keep posting it around and show you what other bits you could get, I have lots of alts and I've lost track of which character has which bits and what I am or aren't missing for future characters.
* Either make flight paths more direct or do away with them and replace them with portals (like GW2 / Rift etc) no one wants to sit there unable to do anything while their character is sat on a mount flying all over the palce trying to get from A to B. I know it's designed to slow people down and make things take longer but it's just silly.
* Add 'Orders' to the Auction House so you can state what you need and what you're willing to pay and people can farm it/make it for you. ie: If you needed 500 Frostweave cloth but don't have time to farm it and the stuff on the AH is too expensive/not enough of it you could put an order in and people can farm it for you while you are doing other stuff/offline.
* OPTIONAL viewing of the trade chat from anywhere. Blizz want people out and about in the world, then address the reasons people stay in Cities, Trade chat, AH and Bank, I agree AH and Bank should stay in the cities but why not make the trade chat viewable from anywhere so people can get into raids/set raids up, sell stuff etc without staying in a City? Just make it toggleable so we can turn it off outside of cities but that it automatically comes back on when you enter a city.
*Why does gear in your bag count towards your ilvl? I mean if I was a DK, I could keep Cloth/Leather/Mail and Plate gear in my bag no matter how inappropriate it is for my class and use it to push my ilvl up to get into LFR etc, it causes people to Ninja trinkets.rings, cloaks and Necklaces in Dungeons as anyone of any spec can need on these items. Cloth characters are at a disadvantage as because they can't equip leather/mail/plate it doesn't count even if they win it on a greed roll/questing loot. Make it so it only looks at your equiped ilvl and find a way to stop people changing gear to manipulate the system, make it more fair.
Ok thats my ideas, I know not everyone will agree but over the years of Playing WoW these are the things that stand out that I'd personally like to see done