I want Franky v Sasaki, Jinbe v Who's Who and Robin v Black Maria to be meaningful fights with deeper connections. The same way Sanji v Queen or Raizo v Fukurokuju is.
Potential ways to connect them:
Franky v Sasaki - Kokoro.
Jinbe v Who's Who - WW's face and their former warlord business.
Robin v Black Maria - Black Maria could be a CP0 agent; I wouldn't mind it.
Nami v Ulti or Usopp v P1 didn't have any sort of real connection. That's why I think Big Mom defeated them instead.
Even if they end up finishing Ulti and P1, it won't be their big moment of the arc, in my opinion.
I don't know what Usopp and Nami will be doing, but maybe they get a moment against Big Mom or the numbers?
I'd like to see Nami zapping Big Mom the way she did in Whole Cake Island, she could potentially be a great help for Kid and Law.
I'd like to see characters outside of Onigashima get expanded a little more.
Hiyori, Hitetsu, Onimaru, and Toko come to mind. We will most likely get that once the battle comes to the Flower Capital.
I hope Ryuma gets explored. For a man who has been made into a National Treasure and consecrated as a god. He sure does feel completely irrelevant in this arc. Maybe we see him mentioned again in a Kaido flashback?