Just spitballing here but they could add a kind of gear mod item to certain dead content. It will +1 your weapon to give it 1 more weapon damage. Depending on the type of weapon there's different caps on how many times you can enhance them. Low item level weapons can accept more.
If V&C dungeons dropped those, they could be part of everyone's gameplay loop. Not a perfect idea I know, but an example of adding new kinds of rewards that aren't just cosmetic fluff. People like to work on something that makes them stronger.
Materia could have unique kinds from specific content such as eurekan materia and bozjan materia. Combining certain materia could create further new kinds. Mutamix could give us a portable furnace as a quest reward so that we can merge materia ourselves at any sanctuary.
