SE said they were thinking about making gear from raids have the capability to equip materia into them. The idea behind materia is to try to balance crafted gear and raid gear so there isn't too much stat difference between them. While I think there should be some crafted gear that is best-in-slot, or at least bis for the difficulty of obtaining, raiding gear should generally be stronger.

So my idea is to cap materia slotting on untradeable gear to one per item and allow crafted gear to retain the ability to slot multiple materia with a low success rate. This would make raiding gear stronger than crafted in most cases but with enough work, crafted gear could be just as good, if not better in rare circumstances.