I'd like a melee/caster hybrid (paladin, spellsword, red mage) but give it enough skills so it can go one route or the other, with the number of skills a char can equip being the limited factor. Maybe give the class traits that can increase physical offense/defense at the expense of magic, and vice versa. Just don't call it red mage. Call them spell blades and let them use gunswords (wand swords?) or something like that.

A summoner/blue mage mix would be good.

Dancers and Bards would be nice but I'd mix the two classes into one.

Thieves.

Ninjas and Samurai would be good (just let samurai use spears and bows in addition to katanas).

A chocobo rider class would be good.

Earlier I suggested a trade class that can create custom dungeons, and I stand by that. I guess a trade class for player housing or custom GHs would be good. Give us a sims-like interface for that and let us build it one section at a time.