Many are rightfully assuming that with Saint Jay Garcia Saturn arriving, he will command the Seraphim to go against the Straw Hats and Vegapunk. It has been said multiple times that the Five Elders have ultimate control, so that’s a layup theory.
What has also been emphasized in this arc is both Bonney’s Devil Fruit abilities and how the Seraphim are in their infancy. In Chapter 1072, Bonney tells Vegapunk her abilities are only temporary.
Bonney’s entire drive right now is to find out what happened to her dad and why. She also attacked Luffy when he went to attack the Pacifista cop, purely off emotion.
Assuming Bonney is still on the island (since Vegapunk mysteriously disappeared) I believe that once Saint Jay Garcia Saturn arrives, he will inform Bonney that Kuma is currently attacking Mary Geoise and that he will spare his life IF Bonney uses her abilities to temporarily age up the Seraphim. That way, he takes full control of the matured Seraphim, giving the Straw Hats as much trouble as they had against the Pacifistas in Sabaody. This temporary age up will give the audience a glimpse of their full power for the final war.
Bonney will do it because she wants to protect her dad, and if/when she sees her dad’s memories, she may be in an emotional wreck and absolutely determined to protect his life, ultimately betraying the Straw Hats.
I am not of the notion that the Gorosei are combatants, so I believe there will be another arc mirror of Luffy punching a Celestial Dragon with him punching Saint Jay Garcia Saturn (this is also another common theory people have been speculating). I think Luffy will do this to try to stop the Seraphim on top of just being angry that Saint Jay Garcia Saturn is using Bonney’s emotions against her.
So the Straw Hats, Stussy and the Vegapunk satellites will be up against the matured Seraphim, Kizaru, potentially Lucci and Kaku if they’re freed, and however many other marines. Even with how powerful the Straw Hats are, I think this is definitely an overwhelming fight. We will see how far they’ve come, but they will still have to find a way to escape or be utterly defeated.