Also polled this one on my brothers guild site. Here are a few of their suggestions:
1) Quests 2 learn other races languages
2) Quests that "help" opposing faction (would work in PVE but I don't think as much in PVP)
3) Recipies to break down items as well as enhance (ie medium leather to thin leather, or elemental earth to core of earth)
4) Engineering belts for engineers to make for carrying extra trinkets or jewelery pins for JC's
5) Improve +healing on JC Statues, gems etc
6) Dye Options: Ie you make a "plain robe" but think it would look cool inpurple rather then black so you buy the dye and use while making!
7) Add a lot of the "oldworld" recipies as trainer recipies rather then drops or rep based
Heroic Instances for top end old world (Stratholme, Dire Maul etc)
9) Additional avenues for gear outside of Bg's or Heroics/Raids
10) water mounts
11) Skill to make regents? ie engineer could make candles, herbalists could grow briarthorn
12) Guild Houses: instanced zone so each guild uses same entry then "add" based on guild contribution with items such as basic vendors, daily "ore" delivery etc.
13) Ability to "scavenge" items - ie you recive a grey item (ie sword) a blacksmith for instance should be able to smelt this down for copper or iron
14) Ability to do more than 1 type of proffession within a tree - ie tobe able to do both Gnomish & Goblin Engineering, even if it means that you need to do both questlines
and a few more of mine were:
1) A mount who you can do battle from while mounted
2) Readjustment fo some quest item drop rates (ie gorilla sinew)
3) Extra points for talent tree (ie at the moment 61 points wont allow u to fully equipa resto tree, but 20 - or 40 - extra points would and would allow you to add a few points to damage dealing so you can survive solo!)
4) An evolving world (send Trolls back to Senjin and Gnomes back to Gnomergan) - though this wouldn't work for thse interested in storyline content
5) Bag slots for your land mounts (i.e a Kodo comes equipped with 2 bag slots for you to use, and epic comes equippedwith 4)