I don't think adding new tank job is a good idea right now.
First, because fixing WAR (why would you give a new tank job to MRD instead of just fixing the existing one ?) is a priority.
Second, because the game is designed around the fact that most "end game" content is supposed to require 2 tanks.

Right now, with the exception of Coil, everything is solo-tankable and people often doesn't want a second tank, thus two issues :

- Harder to find a party (finding a party for Titan HM on my serv is really difficult for a tank for exemple)
- It's a pain in the ass for the tank sometime. Take CM, every DPS want only one tank (mainly because a huge majority of them are bad and can't do their job properly, so they want one more to cover for that) and that's it. Well, as a tank, I dislike solo tanking this place. Farming it isn't verry fun in the first place, but having to solo tank it is just an horrible thing I'd say. There's no room for having fun, you gotta run everywhere to gather adds asap because the -solo- healer isn't smart enough to wait a couple GCD and pull aggro instantly, gets one shot and its a wipe. People want to gain 30 sec with another bad DPS in the group but often can't deal with the second boss and wipe one or two times and ends up losing more time, at the cost of the tank's fun.

And most people you're being teamed with through duty finder are beginner or people that, I suspect, got so much flack for being plained bad in PUG that they decided to run it through DF. So I have two option, running everything as a solo tank, and it's sometime not fun at all, or go with the duty finder and get teamed with bad people/jerk/... It's not a big deal, but when you have to run this place over 120 times to get your accs, it ends up getting frustrating.

So yeah, add more DPS job (easier to play since the already really easy one seems to be too hard for a wide majority of people) and lots of healer job since we seriously lack in that part. This will draw attention on them and fill those empty rank with a really easy solution.