Also If you think releasing XXX class/job as a tank will incentive ppl to become tanks, you're pretty naive.
People who like to tank will tank, people who don't won't because of all the stress involved (brace for the incoming lolDKNs tanks)...most you'll get is ppl who like the class doing the job quest for the story, max... maybe you'll have a small % that discover they actually like or are good naturally tanking, but those'll be the least.

If they don't like to tank, no ammount of DKN, SAM, Lightning-jumping-around, Cloud-using-his-bike, will make them tank.