@Count:
Any length up to ten chapters is possible. I don't think more than that is possible with how centric the story has been on the Straw Hats' adventures despite the insane amount of worldbuilding. It's just that I doubt Oda and his editor would be hyping up Wano Country if it was going to release during the final weeks of 2017. Making such an announcement makes more sense if it were to start during the likes of summer or fall.
I agree, but I would appreciate plot threads like Chopper in Mirror Land getting expanded a bit. And Brook getting a properly difficult fight to invest in for once in this story. But those are personal whims. And the Swirly Hats being out of the story of Dressrosa for about seventy chapters has always concerned me (but then again, those seventy chapters juggled a LOT of characters and plot lines besides the Straw Hats. But the pacing of the arc works out, especially if there is luckily thirty chapters somehow instead of just twenty.
There's still the fate of Pekoms, who probably got rescued by the Sun Pirates. A Jimbei sub-plot isn't completely impossible lol. But I agree about Big Mom as well. Not that she actually gets defeated in a physical fight, but that the tenuous relationship between her, the Straw Hats, and Fishman Island gets solved this arc (as well as Germa 66 and Firetank Pirates).
It's possible. But only at the beginning of Wano Country. In the sort of fashion of how Oda likes to switch the story to scenes with other locations and characters during the transition between the end of the current arc and beginning of the new one. I think he could even do the Reverie in less than five chapters, which is what I've been expecting all along. But the Reverie being name dropped so specifically like that has me wondering…
Reverie is too tricky to be solved so quickly.I expect racial segregation to Neptune and co.,Cobra,Riku,Elizabello all coming to their support,some drama with Shirahoshi and Vivi and more unexpected things.it's been hyped for so long…
Also Oda is more and more indulging in handling multiple stories at once,so it is not that difficult for him to carry two arcs simultaneously.