I like the idea. But it would work with the armory system here. Weapon = Class; Class + Soulstone = Weapon + Soulstone = Job.
They can just make new weapon skins but...
...as more weapon skins you use for single classes/jobs you will automatically reduce the possible amount of weapon skins for new classes/jobs (no overlapping weapon skins between classes/jobs).
...some classes are fixed to a single design of weapon (Archer/Lancer) and if not all can get new skins noone should get new skins.