I have a theory on the XP/Leveling/Job system.
The artwork shows what appear to be several children.
I think instead of levels gained from XP there will be some system where your character ages as they progress. So when you begin, you are a child and as you level you get older. If we get subjobs I would guess that there is some system that takes into account your experience for all jobs when playing a job. Such as, if you are playing your main job and it is capped, you may appear to be near end of adolescence. As you play other jobs, you would get older again. So ever job you capped, the affects of aging would slow down a little more because they wouldn't want a bunch of dragoon's trying to <Jump> with their walkers. Or of no subjobs, maybe every job starts as a child? The subjob theory seems more appealling though.
Anyway, that is my theory.
Remember, you heard it hear first.