Personally I'd love it if they eventually added Bangaa as a playable race. Bangaa and Seeq not being playable in XII was a huge waste ("let's have this amazing fantasy setting with a lot of different races but you only get to play humans and 1 bunny girl"), but Seeq would be very problematic to implement as a race due to their body shape requiring major adjustments to armor.

Also maybe Burmecians but Square seems to have forgotten the rat people even exist.