To be honest, the best incentive to get players to choose tank or healer when queuing already exists.

They get a much shorter queue time.

If I'm trying to top off tomestones for the week and decide to use a roulette to do it, I'm going to go tank or healer because I know I'll get a party faster. That lets me get back to doing other things faster.

AIN only influences which of the two I choose, not whether I'll choose them. The only time I go DPS is if I'm queuing with a group of friends and they're already filling the needed tank/healer roles.