I think this cover will focus on the villains of the arc since its been 3 volumes. Big mom (should be on a volume cover more then once this arc) in the back/middle (possibly in rage mode). Katakuri, since he has been revealed; other somewhat major players such as Perospero, Oven, Daifuku, and Smoothie (she is a commander after all) on the right. The rest of the Charlotte family weren't to big this volume (yet?).
On the left, Du Feld, Stussy, and Big news Morganz with the tomattebako box (not sure if the other two are relevant enough at this point, and to prevent overcrowding).
Luffy below big mom as I don't believe it will be an all villain cover (such as Alabasta, Enies Lobby, and Dressrosa) and Sanji above the title with 3 eyed Pudding.
Color scheme Dark Purple and Blue. :D