May I suggest tabards be made into into a menu like mounts and pets were?
Another thing other games do so well is having a separate storage for quest items. Blizzard used to have a "keyring" for keys before they removed them; do something like that but for quest items please!
Also having to carry x amount of gear can be a pain. Could we please have a tab/wardrobe specifically for that? When dual spec was introduced it slowly evolved so that we got 2 sets of bars corresponding with our active spec. Can this somehow be applied to equipment manager and have it "save" the gear on itself instead of having to carry it around in our bags so it doesn't take half of our bagspace simply to carry 2 other sets of gear?
Toys and other novelty items, can these also have some sort of pet-like list so they stop occupying bagspace? MOP is guilty of throwing so many toys at me that most I had to destroy simply because I had no storage space for them. I want to keep my puntable marmot! Give me a toybox menu!
Those are some suggestions off the top of my head, I don't care how it's done, I just need more storage space please.
A nice suggestion by Heartlis:
At least allow much larger stacks of pretty much everything