I'd love to see some of the old classics return, but mostly I'd like to see jobs which bring their own unique mechanics to the game.

Thief is an obvious choice. Aside from the trademark steal skills they had some unique fighting mechanics which were crucial in some areas of FFXI. Using Trick Attack to add enmity to tanks is one example, and guaranteeing a critical hit with Sneak Attack is another. Combining SA with TA and a powerful skill gave Thief insane damage in the FFXI midgame, easily capable of outstripping even a Black mage ancient magic spell.

Blue Mage is another choice morsel, but only if they set it up well. I'd like to see a return to having to LEARN certain spells rather than have them granted at a specific level. It adds another level of gameplay to the class and gives the opportunity to give rare and powerful skills to those who challenge tougher enemies.