I actually like a lot of these ideas but let me take a moment to pick them apart just to see what your responses would be
Tanks with low threat, but high survivability - The game is presently centered around aggro being generated at a very specific, pre-designed level where holding it should never really be in question. If you're suggesting that the tank be forced to do something akin to FF XI's Paladin aggro rotations which were ability centric rather than weapon skill centric then you're playing a very cautious game of cooperation with your DPS where you're going to be entering periods of lull where you may not be generating any aggro at all relative to your DPS in certain periods of time (I also have to question how effective your cooldowns/abilities would really be if they're being used to gain aggro rather than survive hits). Though you could mitigate this by actually making your weapon skills be what generates your defensive cooldowns rather than abilities. I dunno I'm skeptical about this.
DPS that can transfer hate - Due to the way aggro skills work (Or Paladin's entire rotation basically which consists of only 3 abilities) this class is basically wholly unnecessary, aggro is not a problem in 99% of encounters because it's not particularly designed to be one. In FF XI you could actually challenge your tank's "aggro rotation" by doing Beastly DPS and seeing if they could hold on, not really the case in this game because holding aggro isn't designed to be a "test". The only way this job works if you create other specialized roles for it to work with, which is sort've against the design philosophy of the game which is very much "Insert round shape into round hole, insert square shape into square hole, etc."
Melee DPS with cast times that root them in place - Given the fact that so many AoEs in this game originate or exclusively target around the boss/enemies and people already die in swarms while Dragoon Jumping this could be potentially disastrous, but it also could be fine since we already sort've have the precedent in Dragoon (Though the combination of lots dodging PLUS cast times might destroy their DPS in some encounters whereas something like Turn 8 might make them godly).
Pet job where the player does very little damage and their pet will die to a couple of hits, but does massive damage - Goes against SE's philosophy of "It's hard so we won't do it". Other than that it's fine
Pure Support Class - No complaints
Pure Debuff Class - No complaints but basically impossible to implement for the reason you brought up
Evasion Tanks - Break the game when they're strong (ie can dodge a lot), are worthless when they're weak (when they don't dodge). The best mitigation in the game is not taking damage which is what dodging is.
Debuff Tanks - We sort've already have this? Kinda.
Drain Tanks - They already sort've tried this with 2.0 Warrior and failed really bad before reworking it to resemble Paladin. Not sure how round 2 would go or differentiate itself from current Warrior. Drain tanks are strong in prolonged battles because they get their HP back over time and can recover from small sustained damage on their own. The problem is in this game 100% of the time when you die it's because you didn't properly mitigate the one big hit, Landslide, Death Sentence, Ravensbeak are all examples of this. The Drain tank has to not only recover after the big hit, they need to find a way to actually survive through it to begin with.
DPS that does more damage the more enmity they have - See my comments on Tanks with low threat, but high survivability and DPS that can transfer hate.
Jobs like these worked in older MMOs like FF XI because the game wasn't designed around the "Square shape into Square hole" mentality. I don't see how most of them could work in the game's current approach without some global mechanic changes which is unlikely.