if there's one aspect about old tanking i do miss, it was the passive abilities of tank stances. I would love to see the tank stances return as more than just a blue emnity button. something simple like

WAR- Increase HP pool by 30% and self healing by 20%
DRK- increase defence by 10% and damage dealt by 10%
PLD- increase defence by 10% and block rate by 20%
GNB- increase defence by 10% and parry rate by 20%

something to give each of the tanks more unique flavour by complementing their gameplay.
then we can do away with that awful lv 1 mastery trait that only bloats our HP pools and passive mitigation, thus making active usage of mitigation skills more important again. they could even introduce dps stances with simple benefits to further complement our kits. maybe dps stances change the 1-2-3 into the old emnity combos? maybe certain skills can only be used in dps stance (such as edge of shadow for DRK)
not sure but just something to add a little more job identity back