They kind of already have that. The GC daily supply missions have you crafting something (or gathering 5-10 of that something) and handing it in, for exp in the relevant class and GC seals.

I don't know that anyone at 50 is using those, because the rewards are so crappy. There is an achievement for a BiS crafting jewelry piece but it requires so many hand-ins that most people are content simply pretending it does not exist.