I'd be cool if dragon-form Momo starts creating dragon clouds to stop Onigashima from falling on the Flower capital and suddenly Smoothie appears with the BM ship finally reaching Wano's shores. Perospero may tell her Kaido and Big mom want Onigashima to fall on Wano, so Smoothie tries to attack Momo who's contrasting Kaido's power, but Yamato stops her and they fight. If Yamato vs Smoothie is going to happen before the end of the war, I see no other option, if Smoothie can't reach Onigashima while it's flying.