I desperately want more stat variety. I don't know that we'll ever get items more in the vein of FFXI's (like the items in 1.0), but at the very least I would like to see them add a couple more statistics for gear. Healers already have a 4th stat to think about in Piety, and I'd like every role to have another one to think about, ideally. Buff Parry in some way for tanks (add a counter effect to it or something, so it's not always inferior DPS stats, at least) to give them a fourth stat option. Accuracy could be giving some sort of additional function, as well, for DPS classes (though I'd prefer an entirely different stat—I'm just not sure what would be a good one at the moment).

Some sort of "Mastery" stat like WoW added would also be welcome, which would have a unique effect for each class (scaling appropriately, of course). NIN mastery might increase Ninjutsu damage by some amount, while PLD mastery could perhaps increase block amounts in Shield Oath (but increase auto attack potency in Sword Oath). Those are just off-the-cuff examples, of course.

But gearing is ultimately too simple in this game for my tastes. Most classes only worry about 3 stats, when you get down to it, with two of them being desirable and the other being generally unwanted. With a couple more stats in the mix, gear could have more varied combinations of stats, and potentially allow for the Crit > Det > Speed paradigm to vary somewhat more between classes (I know BLM's preferences are different, of course, but they're one of the few examples of that now).