The 4th Tank.

[Causality]

I'd like to see one who's emnity burst increases the farther away from a target it is, with a proc or CD buff that would ignore distance gap for x amount of seconds. Damage stance could (Like gauss and Minuet) add cast time and Damage increase to abilities while tank stance can do what tank stance does, perhaps a health increase and Healing received increase like Warriors since Dark's stance imitates Paladin's Shield Oath. A Range Rank as it were. We have Paladins with Fight or Flight, Wars with Unchained + Berzerk, and Dark with Darkside.

as for Magic stats, It was said they don't want to make special sets for one tank, so a modifier would be in place so they could use the same Gear as BLM/SMN. The tank stance could convert Spell Power/Int into parry/dodge (I see this being more of a dodge tank) and multiply Defense. The abilities would run around emnity instead of Damage so the potency would be much lower than DPS casters. The DPS stance would increase Damage output to where a Warrior in Deliverence or a DRK with Darkside and no Grit would be. I would say Pally with Sword Oath but they just don't put out.