We have draconic missives, let us apply it to pieces of gear to get the stats we want. Especially for PvP, there’s only a bunch of crit/haste pieces and no mastery allowed.
That doesn’t fit into an ultra competitive game like retail WoW.
You technically can already do it, just requires crafting all the slots which rn is lame because of sparks… and there’s the issue with mail craftables being super expensive mat wise… Requiring the centaur trophies, infurious items.
Congratulations! Work Orders are over there. 
If those didn’t require a bunch of sparks and mats, and you could use your vault for a work order craftable yes. Right now you can’t.