Three concepts come to mind.

"Materia Polishing" the ability to upgrade lower tier materia into higher tier materia through some process so the aspect of obtaining a tier III when you wanted a tier IV is no longer as bad as it use to be since you can just go through another step to upgrade it

"Materia Catalyst" a new accesory slot that allows you to attune 3-5 materia through the purchase of a crafted item to add a bit more customization as well as allow the use of resistance materia to be more viable in dungeons and such

"Materia Overlay" Process of adding materia to unique/untradeable gear via the use of a specially crafted Crafter item which would allow you to add materia to gear which once had restrictions to said manner. However with this process each materia attempt would require said catalyst so the process of each meld would have 3 reuirements, the materia, the catalyst, and the specially crafted catlayst based on the repair class for piece of gear.