Personally I really want a spellblade enspeller Mystic Knight. Ideally as a tank, but I'd take it as DPS, too. Since RDM is more cast based, I'd like this guy to be melee focused. I want his rotation to be using Enfire, Enblizzard and Enthunder then releasing a big attack very similar to SAM Midare of combining all three elements. Honestly I'd love a copy and paste of SAM, put in Mystic Knight aesthetics instead, lower potencies and add utility.

Of course, GEO makes a lot of sense and would be awesome as well. MTK spellblade enspeller is just my favorite job in all of FF.