Summoner is the most likely class to come out. It is the only one that can cover both pet and mage requirements that Yoshi wants to implement.

However, Red Mage also has been mentioned, though there has been plenty of feedback to stress to the developers that Red Mage is desired as a Hybrid class, not a pure mage class, so that might discount it as the mage selection.

I'm not sure how that's going to fit with Musketeer and Archanist, personally. Red Mage is primarily a light-sword type class, and thankfully Paladin sticks with dagger/gladiolus type swords.

If I were to make a call on this, we're likely to receive Musketeer/Corsair(Gambler?) and Archanist/Summoner. Red Mage may come with 2.0 or later.