The future of Thief and Ninja (minor 2.2 spoilers)

[Melinia]

If Ninja did end up being tank, would they have all new armor sets? I mean I can't imagine them wearing current tanking gear.

They'd no doubt have the exact same armor as their starting class in order to make the transition easier. The example we have right now is Scholar, which is a healer that comes from a dps job. Scholars continue to use the same armor as Arcanists, with the same stat bonuses, even though their role has completely changed. But Scholars also get a handy trait that boosts their MND stat. If Ninja is brought in as a tank, then it will probably get a similar bonus in some fashion that will help make up for their start as a dps class.

[Reynhart]

They'd no doubt have the exact same armor as their starting class in order to make the transition easier. The example we have right now is Scholar, which is a healer that comes from a dps job. Scholars continue to use the same armor as Arcanists, with the same stat bonuses, even though their role has completely changed.

At high level, SCH wears the same gear as CNJ and WHM, not ACN.

The other option is for them to implement an ability that spreads damage out on NIN tanks so that when they do get hit, the damage is spread over time so healers have time to react, rather than the tank going from full to dead because of an unlucky streak of no dodging.

For me, the "fine" way to do an Evasion tank is by using short-duration Evasion buffs. Not something like Utsusemi where you create your shadows, and they absorb by themselves, but something more like "I'm dodging the next attack and the effect lasts 3s with a recast of 15s". We'd have a pure reaction tank, that requires a lot of skills to play nice. I think it's fair for it te be a "better" tank if it's far more complicated to play properly.

As for the job/class relation, I'd think Thief as a class, Ninja as a Job, being a DPS, and Samurai as a secondary job, being not an "Evasion tank" but a "Parry tank", with buffs like I described earlier.

Why "Samurai" ? Because Doma -> Cyan -> Samurai

[Melinia]

At high level, SCH wears the same gear as CNJ and WHM, not ACN.

Sure, once everything goes super specialized. But at lower levels they wear the same armor as ACN... and also, incidentally, as CNJ.

At low levels, a ninja tank would no doubt wear the same gear that it wore before becoming a ninja. And once they reach level 50 and everything starts going specialized, they'd most likely have their own unique armor.

We've already seen that with things like Relic weapons, which are Job-only, and can't be used by the original class.

[Reynhart]

Sure, once everything goes super specialized. But at lower levels they wear the same armor as ACN... and also, incidentally, as CNJ.

Because low-level mage gear gives the same amount of Mind and Intelligence, which is all they need.
Low-level tank gives much higher defense and magic defense compared to standard Disciple of War gear.
For example: (lvl30)
Storm's Private Cuirass DEF/MDEF 65 (Tank only)
Storm's Private Chainmail DEF 43 MDEF 22 (Tank and LNC/DRG)
Storm's Private Acton DEF/MDEF 33 (Disciple of War)

And it you would safe to assume that Ninja wouldn't wear the Chainmal, since it's a "light" fighter, like Monk.