Oda never introduces characters late into an arc. He ALWAYS introduces everyone involved in an arc early on in the arc. The people introduced early on are the people who the arc ends with.
People (myself included at the time) thought Shanks would appear in Dressrosa because he was finding Joker difficult, and he never showed up. He won with his own power and everyone introduced early on.
Oda literally never and has never had a character just swoop in late in an arc. Learnt enough from trends that the idea someone will come to save Luffy never happens. Luffy's not at the stage where he needs help, he's at the stage where he proves he's not needing help and is a great Pirate like he promised Shanks he'd become.
Weevil won't be appearing.
The SHs already have enough characters to take on Kaido:
- Law's Heart Pirates
- Kid Pirates
- Nekomamushi who will likely show up with Izzo instead of Marco which would explain why it's taking 2 weeks for Nekomamushi to arrive at Wano.
- X Drake
- 4,000+ Samurai
- Zunesha was stated to be coming
More so, got to take into consideration that there are not only A LOT of allies that need screen time, there are also A LOT OF VILLAINS that need screen time. Adding Weevil to the mix would be excessive and he's not needed.
Further more, if we look at the big picture, Luffy was saved by many powerful Pirates. 2 years later he's reinvented himself and now, he's not asking for helping and owing favours, he's the one being owed favours. Why is that important? The end goal is war with the WG and Luffy needs allies.
Luffy has saved Fishman Island, Alabasta, Dressrosa, Water 7, Zou, Wano soon, WCI (eventually). What is the result of saving them? They became his allies because he's a Hero. Being a hero means he's trusted. Being trusted means if he reveals the Void Century which shows how evil the WG is, these nations will fight alongside Luffy to bring down the Celestial Dragons.
What am I getting at? Luffy defeating Weevil would mean Marco owes Luffy a favour. Not just Marco, but the WB Pirates for protecting WB's treasure, but also, honouring Whitebeard. That would give them reason to ally with Luffy for the final war.
The entire story is literally about Luffy gathering allies for the final war. The arcs we're going through are just establishing his allies. Wano is just one of many, we're going to have Elbaph being indebted to Luffy soon and even WCI (Katakuri seems to be built up as an a potential ally). The final arc will probably be the war.
Weevil may very well show up after Kaido is defeated, but I doubt he'll appear in Wano. Once Kaido is defeated, Wano needs to rebuild, celebrate, and the usual. Can't have Wano being destroyed more after the battle with Kaido.
Big Mom also likely won't feature in this arc much; can't have 2 Emperors defeated in the same arc. Oda will probably meme Big Mom again or have her return to WCI for whatever reason.
