Blue Mage is a minigame...
You level it up, you learn the attacks, you then take it to The Masked Carnivale to earn Gil, Allied Seals and Tomestones of Poetics.


If you want to have your hopes up on it getting to be a real job you're going to have to wait until they have at least built it up to Shadowbringers, it's currently only ARR content. I do believe they have promised to make HW content for it, which'll mean new skills to learn and more leveling, and I would hope with HW content Centurio Seals to replace the Allied ones.
It'll probably be a good while after the release of Shadowbringers if it happens.


So just don't think of it as a "job", think of it what it is... A minigame.