There's no reason to hide the numbers at this point either. Just dump the entire Kaido crew this chapter, show that BM's crew is present (they haven't been seen in almost 50 chapters), and then tease Kaido's Son at the end. I can see it now, Kaido calling his son "Ace".
Hell, give some perspective on Orochi's guards, we know they exist and they've barely gotten exposition (Mimiwarigumi, his possible Retainers, and maybe the Shinsengumi if they exist)
Should be a wholly exclusive Kaido-side chapter.
What? That's like in 22 chapters, what are we going to have before that?
Can't be a flashback, too long for one and we just finished one 5 chapters ago.
They can't talk and sit on their asses for that long now that the alliance arrived at onigashima.
Chapter 1000 is reserved for a bigger event.
You underestimate Oda's extension of battle setups.
- Enies Lobby spent like 25 chapters setting up the CP9 battles and getting everyone in their respective places
- Dressrosa spent more than 30 chapters doing the same thing before the family went down.
They haven't even arrived at the Onigashima Port, then Oda has to show 4 different perspectives initially:
- Luffy and Kid barging at the front door and likely destroying fodder
- Kinemon's side in advancing through the Onigashima mountains
- Denjiro's side
- Law and the remaining scabbards doing a surprise assault from the rear (they will likely get there first if the distractions work)
Shishilian and Hyogoro are likely with Kinemon/Denjiro somewhere. Kinemon/Shishilian could lead the Minks one way. Denjiro/Hyo would lead the Samurai the other way.
Additionally, Oda has to characterize like 30+ villains before they get defeated, we will see a TON of skirmishes I'm sure. He also has to probably do a Rocks flashback, it will happen before or after the War starts. Luffy and crew need to steal the road poneglyph, save Momo, the scabbards and crew need to confront Orochi/Kanjuro.
There's so much that could happen before the main battles start, that I'm not even sure 22 chapters will be enough to do so considering how Oda writes his scenes. Chapter 1000 will probably be the arrival of some major character (Perhaps the one talking to Crocus in that one cover page?) right before the end of Act 3 or something. But I don't think the actual war is starting until after this point, imo.