Forget blue mage. When do we get red mage?

That said, in the third Live Letter From the Prodocuer, Yoshi-P confirmed that second jobs for each class will be released at some point. The battle team has put its efforts into re-designing and re-balancing the existing classes and jobs, so they're holding off on adding more into the mix. That said, I expect that secondary jobs will play up their base class's abilities that the existing jobs do not. I expect the breakdown something like as follows:

Gladiator > Paladin (Tank) / Dark Knight (Damage Dealer)
Pugilist > Monk (Damage Dealer) / Puppetmaster (Pet Class)
Marauder > Warrior (Damage Dealer) / ??? (Tank?)
Lancer > Dragoon (Damage Dealer) / ???
Archer > Bard (Support) / Ranger (Ranged Damage Dealer)
Thaumaturge > Black Mage (Magic Damage Dealer) / Red Mage (Support/Debuff)
Conjurer > White Mage (Healer) / Geomancer (Damage Dealer)
Arcanist > Summoner (Pet Class) / ???

The paladin/dark knight dichotomy is too obvious to pass up. Puppetmaster was the top-requested job on the forum, and automatons already exist in the game. Black mage takes no advantage of thaumaturge's innate enfeebling magic passive traits, so red mage is likely there. It's also possible that dark knight gets pushed over to marauder, red mage to gladiator as more of a melee mage, and then have thaumaturge introduce green mage a la Tactics Advance. The bard/ranger thing seems pretty obvious. Given that conjurer gets water/earth/wind elemental offensive spells, geomancer makes good sense as the offensive alternative to white mage. Your guess is as good as mine for lancer and arcanist. I expect thief (another highly requested job) to come into play somehow, probably by first introducing a new base class. Ninja and samurai are obvious at some point, probably coming from a new base class such as ronin. Since they're moving ahead with arcanist, we may yet see musketeer as a playable class, eventually becoming corsair.

I don't know where blue mage would fit in, but I imagine a new class would probably precede that as well.

I like speculating.