An Onion Knight style class that gets stronger based on your number of level capped jobs would be interesting. No idea how that would fit into the Holy Trinity, though.

If Geomancer makes it into the game it should be the other CNJ job, seeing as CNJ is pretty much already Geomancer with a Cure spell. I'd like to see a focus on adding more "classic" jobs first. Like, finish off the list from FF5 before anything else, minus stuff that will never happen like Mime and Mediator. Mystic Knight? Hell yeah.