The first few pages- Ace calls for Kaido at the entrance of Onigashima, destroying a dragon statue in the process. He wants to fulfil his quota of challenging all the emperors and taking revenge for Tama
Middle parts of the chapter- Kaido beats his ass, but is reminded of a young Roger after taking a close look at him. He asks Ace to join his crew but Ace refuses and gets imprisoned. Most of Yamato & Ace's conversations take place here. Yamato frees Ace and he proclaims that what he couldn't do, his brother would at some point in the future.
Last few pages- Transition to present where Luffy is either obstructed by Jack or is shown one shotting him.
This is the probable direction 999 could take. I hope that there would be more to it than just something along these lines