If we look at the proportions of the classes, and what SE has done up til now and where the story will lead to, we can predict a little.

3 tanks, 3 healers and 7 dps

I'd start with the tanks or healers.

Then next step, what has SE already done? The samurai is already done to be implemented. A visitor from doma could just clear that, since we have connections for this possibility.

What could be a healer then? The surgeon could be a completely new healer class, with syringes crafted by perhaps a cooperation of the Chemist guild master and the garlond metal works.

A DPS should be red mage from ala mhigo or a traveling swashbuckler or a new class guild for the ishgardian nobility, since they want to share their knowledge now or something.