Face it: WoW crafting is boring. Learn a recipe, put in the materials, click to create. Repeat again and again to skill up and get new recipes. The end. We have exciting-sounding skills such as engineering and alchemy, but we have no experimentation and little customization! While we've gotten crafting dailies to make the skill-ups a little more fun outside the usual materials grind, Blizzard should probably update how crafting skills work.
Personally, I'd love a system that favors some creativity. Imagine if materials for alchemists were in certain classification: increase or decrease, physical or mental, strength or speed, endurance or power, etc. If you mix an increase reagent with a physical, mental, or power one, you'll make a strength potion. Choose decrease, mental, speed, and endurance, and maybe you make a consumable potion that lowers mana/rage/energy/runic power/focus to targets within the blast radius. No premade recipes, just players experimenting with the game. I can see a similar situation for cooking (mm, spicy chocolate gator bacon!).
Gathering could be redone a bit, too. Imagine if you could break down items to get certain materials, sort of like enchanting. Skinners can break down leather for rare hides, miners can melt down armor to retrieve rare minerals, herbalists could ... pick mushrooms out of pies?
What would you like to see change in WoW crafting? Dyes added to change armor color results? Choosing blades and hilts when crafting a weapon? RP leather armor and whip options tied to custom emotes for those nights in Goldshire?