Something I've been tossing around in my head is the idea of a mage tank job (I think they tried that in FFXI with rune fencer) my idea was a job called Invoker which works much like a summoner but instead of drawing the power to an outside force (evocation) they draw the power into themselves, much like Ultima weapon did. The job would use mp for it's abilities with stances like Ifrit for DPS and Titan for tanking and basing a lot of other attacks on all the primals or at least the 6 elemental ones.