@Kachi,
I've always like the materia system of old. I like the idea of the materia grid, if I can switch it up. For example, having a system where one can choose which slots to link, or multiply, would be awesome. Whether that is done through "basic" gear acquisition, spending points similar to merits, or even just done on a whim. Locking me into "slots A and B are linked, C multiplies, and 4-6 are stand-alone." = No thanks.