Square has a ton of FF games to use as reference for a Geomancer class, even outside of XI. FFTA2, FFEX, I'd say take elements from all of them and make something grand. Honestly, there's nothing stopping them from just being foreign Geomancers from one of the regions we haven't been to yet or even from the First or another Shard. Between that and the actual in-game differences we've seen between Geomancers, if they really want the class in the game they'll have it in the game.