Could see this being partially effective, of you're doing your roulettes as a DPS but you're down to play multiple, you could select from a variety of different DPS jobs and see what one you get.

However, don't see this being effective at all for roles if you select tank, healer, and DPS, you are never ever going to get DPS due to how in demand healers and tanks are.

Still though, I think it'd be a good addition, sometimes I can't make up my mind about what DPS I wanna queue as, I know there'd be others who would be like that too.