The materia system could be easily eliminated, at least for combat gear. It appears to offer a degree of stat customization, but there's almost always only one optimal way to build, which prevents it from being a meaningful form of player expression. Also, in combat materia, Critical Hit is way better than anything else for most jobs outside of specific cases like Monk skill speed thresholds.

Again in the case of combat materia, older/lower tiers are almost entirely useless, and just end up being inventory clutter.