Since the devs are adding materia, how about a new system where you can fuse materia via crafting to get more powerful versions or versions that don't appear on their own. Example, having one weak materia of every type that adds damage, you can get an astral or umbral damage materia.
Other materias could be things like HP regen, bonus TP from actions, MP regen, ignore phy or magical defense, DoT, WS and spell duration length increasers, etc.