You have one. It's called warrior, both their stances are offgcd. If you start in Defiance, do a GCD and activate deliverance, Deliverance eliminates the Defiance Debuff. Similarily, you could make swordoath OGCD and make its activation eliminate any Shieldoath buffs. So the system to implement that is already there.
Which was exactly my point? The point that PLD's current iteration of swordoath is unnecessarily clunky and thus should be changed into something more fluid like DRK's method of turning of tankstance. Which is exactly why I'm pretty fine with the suggestion you posted as well. Systemwise, DRK has a more fluid way in switching from Tankstance to Non-tankstance/Dps-stance, and systemwise, Paladin should be changed to have a similarily fluidway of that particular switch.
Eitherway, you should probably stop initiating talks about Systemlimitations here.
Neither me, nor probably you are Developers of the FFXIV DevTeam, and thus, starting a conversation about systemlimitations is just initiating an uneducated debate between a man with no facts against a man with no facts, entirely meaningless and a waste of textspace. UNLESS you have a specific official Dev-comment that you can derive your concerns from.
The only thing endusers like us can do is talking about how gameplay feels and what we do not like about it. It is the devteam's job to make the system work around gameplay and gameplay adjustments and we should not limit our complaints to what's feasible to the current system exactly because we do NOT know the current systemlimitations ourselves.
If they say it's currently not possible due to systemlimitations, fine, but until no official word has been said, any complaint is fair to be voiced out and should not be dismissed by "It MIGHT not work in the current system, I'm not a developer though, so I have no clue", because that could be said to literally everything and any suggestions, and provides no meaningful argument nor contribution to the actual topic.