With all the buzz about Blu from SE's letter and the Astro quests, I do hope that it is a thing they are working on. I would like to see it as a tank as well (Twelve know we need some tanks and healers in que).
Stormblood spoilers here!!!
And, if they were added, I would honestly see the job teachers either Raubaun (he does a ton of primal abilities in the tourney of HW and of course his name is a big flag for us who played FFXI), or even the warriors of the Steppe. Magni uses some Titan-esque moves and his axe looks like the Crag axe. And then there is Sadhu,
and boy does she scream Blue Mage! The line AoE is Garuda's wind blast, and she summons those Chuluus to spit fire and summon a meteor.
And as for another job, I would like to see Dancer come in as a healer that can heal through dps via Drain Samba. Of course, it would still have direct heals, but it would do good to not have a repeat of Astro's mechanics and have a healer with its own style.