Dammit, I had a huge post and accidently erased it, I will try to rewrite what I wrote.
Now, what I was trying to say with the final fantasy: tactics type of unlocking new jobs, (some of the base classes, mainly DoM would have to be renamed conj= whm or blm) gladiator in combination with either black mage or white mage would unlock paladin or dark knight respectively. But not too ignore base classes. Lets say I went ahead and opened up Paladin, we could give paladin an AoE provoke which would bring a "group" of claimed mobs to the paladin, but gladiator could be an off tank, useful for both pulling hate off of mages and for casual players trying to exp alike. Now the AoE provoke would be unlocked using the talent tree sytem. The talent tree system, I'm not really too hot about, but it's there to appease a majority of players that believe that the only system of fixing the current classes. Now let's say we put in talent tree's to the base classes, we would have to get rid of the armory system. A slap in the face to the old dev team I know, but a change I feel is needed none the less. Alright, so talent points in the base classes= marauder being able to hit more than one mob at a time with talent tree spec in it. Now some of the "lesser known" final fantasy classes could be spec's within the current classes (think pirate, berserker, things of that nature) but letting the "well known" final fantasy classes be unlockable jobs.
Now to adress the Dark Knight tanking, I only used it with a static after reaching level 75, but it could be done. I used absorb vit and absorb agi, gaining large amounts of hate and boosting those stats which were lacking. Giving them a "talent tree" which would boost those abilities which would be useful in tanking (albeit in a "dark" manner) is still a good idea.
Again, most of my idea's are based on the idea they get rid of the armory system. If they don't get rid of the armory system, my idea's are invalid. But, maybe...the dev team could implement better than a guy giving idea's off the top of his head after a few glasses of wine and a 2 year old whining for more word world in his ear.