I think this is a good idea, but may want to have them create weapons other than instanced ones that already exist.

This could be a questing side event whereby you upgrade stuff through morphing it via materia. Once it has the materia on it, it could change when its spritibond fills, and maybe have a specific path of materias to upgrade and slowly create better and better weapons. (with the final tier being oh my goodness, since it would take time)

--> quest for a beginning weapon, do the event that drops the materia, acquire and have someone meld, play with it until morph, then get the next materia that it goes with

just another idea to flesh it out