With regards to how Warrior was restructured over, arguably, one mechanic in BCOB T5 (Death Sentence) and one primal (Titan Hard Mode) I'd wager that in light of A4S catering to the gimmick that Dark Knight brings, I can confidently say that yes it does warrant a restructure. Warriors were in the same situation we're facing now in that they needed to be full i90 in order to stand a chance, yet somehow everyone passes Paladin over because it's the "simple" class. Funnily enough any time anyone suggests making it more difficult to play many, many people outright shout the suggestion down by saying "no Paladin needs to stay simple." At what point will a decision be made to give Paladins more than just a band-aid solution while players constantly say the class is boring......? There are few things a Paladin brings to the end game raids in order to justify its raid slot (Divine Veil for every other major AoE attack that only protects for 1800 damage, Rage of Halone for its Strength down has some use, Cover has only extremely limited uses as compared to how it was used pre-Heavensward, if timed perfectly Clemency can help but it will be interrupted by even an auto attack over 3500 damage....and that's it.)
It can also be argued that Dark Knight is in the same position Paladin is in, however, in a game where DPS from all jobs is paramount, they'll still be of value even in an encounter that doesn't explicitly favor them. All tanks survive the end game raids equally, yet somehow Paladin's "mitigation king" status is the justification people use for them NEVER being tweaked beyond enmity and potency enhancements. End game raiders and casual players alike are BEGGING for more to the Paladin job and it's not just because they're bored of it....everyone views them as the least involved tank. It doesn't bring as much ability to assist the entire raid team as the other tanks possess currently. The fact of the matter is, Paladin will always be the simple tank in comparison to others because of this circular logic. It isn't allowed to grow and flourish to use all of its abilities fully (whether in a MT or OT position) because the community as a whole will not allow it. It's "supposed" to be the simple job, right?
You argue that too many classes already rely on debuffs/buffs to manage that would cause catastrophe if allowed to expire....welcome to Ninja, Bard, Machinist, Paladin, Warrior, Dark Knight, Monk, Black Mage, Astrologian, Scholar, and every other job in the entire game, because they ALL possess such abilities (some even have the EXACT same function and timer.) Homogenization is here by that logic.....a hybrid stack is exactly that, it's a combination of two pre-existing mechanics combined to form an entirely new mechanic. It wouldn't function like anyone elses abilities in the game because I would have to build up stacks in one stance explicitly for the purpose of using it in the other; in fact, I wouldn't be able to access them any other way. Warrior doesn't function like this, their stacks are replaced accordingly and they can continue building the opposing stack. A Paladin on the other hand, uses up his and can't even start from the bottom again because he has to build those stacks in the opposite stance. This would add only one step forward in the complexity of Paladin. We would still be leaps and bounds away from the skill required to play Warrior and Dark Knight.
EDIT: Make no mistake about this, I am glad that Warrior and Dark Knight are where they're at right now. I, just like many others here, just want to see any combination of the three tanks be used in bleeding edge content clearing groups. Currently unless you are at maximum item level you and the bleeding edge content clearers will not bring one of those combinations (DRK/PLD) to end game for progression; in some cases you won't bring the one that clearly under performs at minimum item level (PLD.)