This idea is directed towards fights like Ifrit and Titan, where two tanks aren't actually required. In Ifrit's case, the only reason the two tanks are viable is because one is just a stun bot, while on Titan he is just being a gimped DPS. This means that one of the tanks ends up being a burden, which is bad design.
This idea is gonna assume that SE is gonna keep the rigid 2 Tanks, 4 DPS, and 2 Healers set-up for all of the DF encounters, and it's mostly directed at Warriors, since Paladins have something similar to this already.
Give Warriors a proper non-tank stance
Hear me out. I specifically say "Non-tank" stance rather than "dps stance", since the idea isn't to make Warriors match-up with other dps, but, rather, let them be less of a burden to DF parties when they aren't gonna actually be doing their main role (i.e. Tanking), and at least do sufficiently more damage than the main tank. This way, SE isn't pigeon-holed into ALWAYS looking to keep tanks busy, SPECIALLY when Crystal Tower comes out and you have 6 tanks going around.
You bet some of those tanks aren't gonna be tanking on some points, why not give them a tool to let them make a significant contribution to the raid, instead of leeching, doing trivial dps, while they wait for the moment to tank, if there is any?
Now to address some points:
-I'm aware Warrior has something that kind of tries to do this, Unchained, but, let's be honest, it does not the same job for Warrior like Sword Oath is for Paladin. It blows, should be buffed, or should be turned into a difference stance all-together. If this does happen, my issues would be mostly solved.
-Yes, I understand that this is dangerous in a way, since, if tank unbalances happen, like, say, Paladins are always preferred, there'd be even LESS reason to use Warriors as MTs, since they might aswell just stay doing average dps than being a mediocre tank. I understand that this can be an issue, but it can be fixed if Paladin + SO and Warrior + Unchained dps is well balanced. Also, the idea isn't to design encounters to take advantage of this new idea, but rather to have a back-up plan to fall on when SE designs an encounter where an OT isn't needed, but you still need to q with two tanks.
-There's also the issue that Tank classes inherently create more enmity than other classes due to the nature of their weaponskills, this could be easily fixed if mentioned stances nullified enmity bonuses from their weaponskills.
What is this trying solve?
When content gets harder, the community will value efficiency over everything else. If SE keeps designing encounters that only requires one tank, but the DF needs 2, you will have situations like Titan HM, where going with the DF you are guranteeing yourself 1 Tank, 4 dps, 2 healers, and 1 gimped dps, essentially, which is why many people will favor forming groups outside of random DF, looking only for 1 tank, making tank's chances of getting content done slimmer. This will only get worse when CT content gets harder and SE doesn't assure a reason for 6 tanks, or encounters that don't justify 2. In clearer words, encounters with DPS races that only requires 1 tank, but DF looks for 2 tanks, is bad design.
My two cents, feel free to critique or discuss these ideas. They are more than welcomed.