Messing with elemental resistances etc etc would pretty much require Square to redesign the entire game, not just a few classes. They would have to implement this into every mob, every boss, and then completely redesign every class to enable them to fight with the resistances and strengths.

I don't mean to shoot down the idea, but it's just something I don't see happening, although of course there are many other QoL changes we could hope for.