Nothing of what OP suggested actually fixes what's wrong with tanks in this game. I main tank for my coil static as WAR and PLD. Tanks can DPS just fine. Outside of main tank in Garuda Extreme and Twintania or either tank in Ifrit Extreme, i90PLD and WARs can put out respectable DPS if they know how to. In fact, Yoshi's mount suggestion might actually help fix things because it would at least get people leveling it in duty roulette to 30 (where tanks are short supply). But nobody plays tanks @ 50 for a few reasons.
First, its just plain boring. PLD has 5 effective weaponskills outside of utility ones like Shield Bash/Lob. Only 3 of which get used regularly. Warrior at least has some more going on with a hate combo, and Storm's Eye/Path. PLD doesn't.
But more than that, with the exception of Turn 4, Turn 5 (if you're solo tanking) or Garuda Extreme as main tank, every endgame tank fight is just flat out boring. Your co-tank gets to 3 stacks? Swap hate. Done. That pretty much describes every fight except those I named. Then there's CT where one of the fights literally has you pushing a button and doing nothing else as off tank. The other fights are equally as uninteresting and granted CT is a snoozefest on most jobs but tank is far and away the most superfluous role in CT. There's a reason why party finder groups always fill tank roles last for CT.
But in the rare cases I mentioned where endgame tanking isn't boring? i.e. Garuda Extreme main tank, Garuda HM main tank, Twintania solo tank, Turn 4 + 5, etc? It's really hard in a way that it isn't for other roles. There is no learning curve and in a party finder/duty finder group its possible for a sub par DPS or healer to get carried and it not to be obvious to anybody but the co-healer or someone who is using a parser. Its possible for a first time DPS or healer to just skirt by unnoticed in a fight like Ifrit HM, Garuda HM by just following someone and mimicking what they do. Tanks don't have this luxury. If a tank is bad or not used to the fight? People notice and in a pick up group they get called out and receive more trash talk and hatred than any other role in game. Even in fights that are boring as tank like Ifrit HM, where you are responsible for hitting shield bash only as OT, if you can't do that on your first time you're the subject of ridicule and hatred because you caused the wipe. Tanks have an unfair burden where because of how fights have been designed, they are expected to understand the mechanics of a fight before they step foot into it the first time in a way that no other class does.
And in the specialty fights where other jobs have a harder role than normal you can see that too. Before enrage swept T2 PUGs, bards were always the hardest job to get ahold of alongside tanks. Why? Because they face the same ridicule and abuse if they mess up High Voltage silencing. Ifrit Extreme groups are most often waiting for healers over even tanks because it is the most stressful and hard fight to heal in the game and not understanding how Searing Wind works will wipe successful parties even if you can manage healing through 16 nails exploding.
Even the rare fight where tank has the easiest job (Titan HM) what happens? Jokes about how easy tanks have it with images on Reddit about how the rotation for tanks is "Just stand there" while not acknowledging that Ifrit HM as OT or Garuda HM as MT is as rough if not rougher on the tanks than anything Titan puts out. The difference is that a mistake by the tank in those 2 fights will 100% wipe the party while a mistake by healers/dps in Titan can but won't always wipe the party.
Unless they change fight mechanics to make fights interesting enough to tank to offset the pressure and ridicule you face as tank when you mess up nobody is gonna keep playing them.