A monster or non-humanoid of some description to join the team.
Zero's a part of the way there, but come on. Where's the Red XIII/Nanaki, or Umaro, or Quina, or Construct 8 (not the same 8 but you know what I mean)?
Hell, I'd even accept just a party member that filled in with the rest of the humanoid band if they were weird and out-there in some fashion, like Gau or Relm.
Fuck, we have canon ones already. Feo Ul has literally been begging for a chance to wreck face. Stop trying to make me a god damn tsundere and let me call on the fairy. She can be a dual-purpose White Mage / WHM-themed Magic DPS.

edit: removed Fusoya, forgot Lunarians were effectively just moon-people.