Diabolos would be neat, although they already gave his outfit away with The Cloud of Darkness.

I think I'd prefer a chaotic boss fight against Mustadio or Agrias over Cid...or maybe just put the 3 of them together. Honestly, if there's any Ivalice fight I kind of want to fight, it would be Yiazmat just because I love his voicelines.

Also need a Nald'thal fight where a 3-way scale mechanic exists for the entire fight but forces you to move between the scales to keep things balance based on what mechanics are going out.