At this point I am expecting:
- Egghead 60ish chapter
- Elbaf 60-80ish chapters
- Final war arc (assuming it comes after those two) 80-100 chapters, if Oda wont mess around but uses the other islands straw hats travel for lore, fleshing out some other characters etc instead of dumping everything in the final war, depends how they play out
Id play it out more by islands, because its clear we need to go to Lodestar (where all the islands merge) then beyond that, Laugh Tale. Nothing states Im or Akainu would leave their respective base of operations. Plus, theres too much building up to Fullalead at this point too. Then, you have to factor that Luffy took the most indirect route from Wano, which means more islands to catch up to Kid and Law.
Imo:
- Egghead: 40-50 chapters
- Something Underworld related and/or Fullalead: 40-50 chapters
- The vice versa: 40-50 chapters
- Elbaf: 60-100 chapters (because im not sure how big this arc will be)
- Lodestar: 10-20 chapters. Short, transitional to Laugh Tale.
- Laugh Tale: 60-80 chapters. A BB or Shanks centric arc imo.
- Final War: as you say, 80 - 100 chapters or more but split between New Marineford and Mariejois.
So anywhere between 300-450 more chapters imo. Either as long as what we got from Zou to Wano or PH to Wano. Thats what I have currently based on what has been teased and what we know. I do have this funny feeling that God Valley will also be shown somewhere and used as an arc backdrop, just not sure where.
And sure, maybe this is too much or too optimistic, but its just a gut feeling I have. We still have 3-4 more islands before Laugh Tale personally.