I can think of a ton of things that could be done done to make the tank jobs more interesting, but at the end of the day, if your encounter design is boring then everything is boring. Tanks in FFXIV have potential. They could bring back aggro combos and ditch stances entirely. Throw in aggro decay and aggro resets. There are a ton of ways you can play around with making tanks care about the enmity gauge on the party list again. It won't making tanking interesting though if the encounter design remains the same. Encounter design is the single biggest issue in FFXIV's combat design.