You can breakdown the main participants present on Wano at the moment into three factions
- The Ninja-Pirate-Samurai Alliance.
- The Orochi-Linlin-Kaido Alliance.
- The Wildcards" (Denjiro/Kyoshirou, Hyori, Drake, Caribou, Law).
The narrative could shift towards various possible scenes depending on what is dealt with first.
Scenario 1: If it's to clarify how the plan is still on track, then it'd focus on the Pirate alliance and any of the wildcards that helped them orchestrate the failed planned meeting diversion. Maybe Caribou's power is used to hide the real ships/sunny/fighters. Maybe Denjiro used his control of the Capital to create a new meeting point. Maybe Law or Drake had a new plan.
I'd say that scenario is unlikely since it's best to set the stage at Onigashima first before crashing the party
Scenario 2: If it's to start the festivities, then the focus would obviously be on Orochi arriving, Kaido and Linlin interactions and overall layout of Onigashima.
I'd say this is the more likely scenario.
Extremely unlikely Scenario 3: If there're a few scenes to wrap up the loose ends of the past timeline and act 3 ends mid-chapter, the focus could shift towards around the world developments.
I'd say it's extremely unlikely that act 3 ends with the flashback's end, but if it does, maybe a Sabo update cliffhanger?
TL;dr
Most likely the start of the festivities, Linlin-Beast pirates interactions and Onigashima layout.