Looking forward to Bahamut Ultimate in 4.11, but after that, would like to see who else will have an Ultimate mode. The ones I would love to battle in Ultimate content:

Raubahn and Pipin: Just Kidding, probably won't wanna endure that again.

Zenos Yae Galvus: He's a fun boss to battle against imo. Plus, iirc, the only Garlean who has at least one hard content (including the legacy) is Nael Van/Deus Darnus.

Ozma: I bet that battling him in harder difficulty will be a living nightmare. But that would make him feel like a superboss again.