Make up a feature that you would like to see implemented into WoW.
Mine (I think I've posted this before, but...): I would really like to see some sort of "Account-wide* materials/BoE gear bank" implemented. It would store all non-BoP crafting/profession materials so that all your characters can easily access mats that all your other alts have gathered without having to mail everything back and forth. It could have different tabs for crafting materials from different professions.
*'Account wide' in this case would be limited to all characters who are on the same server/faction, obviously.