Just reposting from the Jump Festa thread thanks to the new info received from the wonderful Sandman about us seeing the Reverie this year.
For a very long time since Fishman Island many people assumed the coming Reverie would happen at the end of the series right before or after the final world war.
There are a ton of scenarios Oda could come up with to get the Straw Hats over to Mariejois just before the war with Kaidou. My guess is that it all comes down to Fishman Island and its connection to every major happening at the moment. It being Big Mom's territory, Kaidou learning that an ancient weapon is located there and the topic of immigration at the Reverie itself might all play into a side trip before the full on emperor show down. I feel like before the take down of Kaidou, the major act that the Straw Hat Fleet pulls off will be some demonstration of power over at Mariejois. Thats just a wild guess of course.
EDIT:
Just to add a bit more, I have a feeling that not only will Kaidou learn of the Ancient Weapon secret but others at Mariejois will as well. I could easily see the Marines, The Beast Pirates and whats left of Big Mom's pirates sending in their own forces to take control of Fishman Island as well as attempting to take control of Shirahoshi. This doesn't mean Kaidou, Big Mom and Akaiunu will all personally go down and get into a fight, they just send a nice sized amount of people to take control of and occupy Fishman Island.
At this point the word gets out and the Straw Hats and their grand fleet make their way back to Mariejois/Fishman Island and Luffy fulfills the prophecy revealed by Sharley. Luffy makes it so no one can have Fishman Island so he makes the conscious decision to completely obliterate the island while getting the entire Fishman Island population on Noah and they make their first real steps to migrating back to the surface and integrating with the rest of the world.
This could be the first major incident the Straw Hat fleet causes that rocks the world.
Or maybe It will be 10ish chapters with all "Straw Hat Nations" being the full on heroes aiding the Neptunes and their cause. Mostly political acts of heroism of course. But man we have our chance for a full Vivi reunion and I'm thinking even if its just for a Coby style chapter or two I feel like Oda would want to give us that before the series finale.
Speaking of Vivi, because she is an honorary member(5.5 I think?) never to be forgotten in our cover pages, I do believe it's because of her that Robin has not received her 6th Person chapter. Robin might harbor a bit of guilt over her actions that were against someone that each of the Straw Hats at the time dearly loved. Robin is totally committed to everyone sailing on the Sunny but maybe she needs a little peace of mind by just apologizing to Vivi.
Edit:
Didn't realize I said a lot of this just 6 months ago. ¯_(ツ)_/¯