Evolved Mode feedback.

First off I am a Gun-breaker main and Warrior is a close second. And I am very concerned that if you separate the tanks into two categories then when an off tank ques into a raid Roulette then the group will complain if there is all ready an off tank and vote to kick. This also feeds heavily into the elitism that is still there in game. If I try to get a group via the party finder and the group all ready has an off tank they will not take me. This change in my opinion will cause a negative reaction if you are not on a Paladin or the new Tank. Which I am not a huge fan of caster tank Paladin as it is.
Secondly with White Mage. I remember a time not long ago when White Mages in particular were in raid groups padding their dps and ignoring healing. This was fixed, but it seems like you are going down the same road again. Are you sure you want to deal with the backlash again?

I've played since ARR and I'm telling you, that won't happen. Nobody cares who the main tank is in queue-for content. I have the 10,000 duty achievement - probably twice over if it would show, so I have more than enough experience to say this.

Now let's say a PF already has an off-tank. Whether they will take you, will depend on a few things. First, whether there is a % bonus for having a MT and OT, or whether the bonus is just for "a tank". Precedent says it won't distinguish between MT and OT for the damage bonus. The second thing is whether the fight specifically depends on something only an MT can do. If none of these things are the case, then 99.99% of PFs won't care if there are two "off tanks", and this is the most likely scenario by the way. Off tanks have to be able to tank since they need to work in 4-person content like dungeons and criterion.