I think they should add a new NPC, much like the Guild Wars 1, Festival Hat Merchant…. I like these new achievement-type items, such as the new back pieces, but the downside to them you only get one, when you have one of every character, its hard to decide what one to use the item on. In Guild Wars 1, the festival hat merchant you take a special item to him, and he remembered it for you so you could have it on all your characters.
Naturally not all items would be allowed inside of that, but items like the Celebration Hat and Devil Horns (free items from the Black Lion items long ago) should be added to the list of what the NPC can make, there basically Festival Hats, along with achievement-themed, items.