Firstly, this is pulled from my reddit post I had just made (I am Paperchampion23) : https://www.reddit.com/r/OnePiece/comments/51szfg/what_do_weeble_straw_hat_grand_fleet_mariejois/. I usually post some fun stuff there, but have been a user here for almost 10 years now and wanted to share something with you all. If this doesn't deserve its own thread, just move it to the theory thread I guess. I don't exactly provide proof, but after reading one piece for years, you just get these feelings of how things may or may not play out. Let me know what you all think!
So, considering One Piece, on its bare bones, is mostly comprised of masterfully crafted rescue arcs that revolve either around people (Ace, Nami, Robin, now Sanji etc) or a Kingdom (Alabasta, Fishman Island, Dressrosa, and probably Wano in the future). I am sure most of us agree that the the average one piece fan does not find this boring, (albeit, there are "some" issues here and there, I'm sure we can all agree) simply because Oda finds really awesome ways to make each arc feel fresh and interesting.
But, what has one thing Oda hasn't done as a result of all of this? A Luffy Rescue Arc
Hear me out. I am fully sure an arc like this won't happen until 2 things occur, when the Reverie is literally almost upon us (like several days, or chapters out), and when the Straw Hats all are together again. That means, based on what I think, the Reverie and an arc like this won't occur until after Wano. I don't think Luffy is going to take on the Yonkou just yet, I'm like 90% sure this current arc is solely about the Vinsmokes (while building up Big Mom for later) and Wano focusing on this Shogun whose killed Momonosuke's father (while building up Kaido for later as well), with whoever decides to join the crew during these two arcs.
SO GETTING TO MY POINT I think Weeble was introduced at the exact right time. He is currently after Luffy the same way Blackbeard was in the past. I think he's going to show up at the worst time, probably after Luffy takes out the Shogun/saves Wano, wreck Luffy and take him to either the new Marine HQ or Mariejois. Luffy has never been captured before, and not once has had to rely on his crew actually rescuing him (discounting Sanji doing so in Alabasta).
So kind of how we spent a huge portion of the story following Luffy saving Ace, I think a decent chunk will be spent on his crew doing the same, assaulting the New Marine HQ + Mariejois during the time the Reverie sets foot. Luffy also has numbers now, so having his Grand Fleet come in would be plausible.
Now people might ask, why would Weeble do such a thing and why wouldn't Luffy be set up for execution? Firstly his mother wants the bounty money, so he'd get captured. Second, remember what that Tenryuubito Saint Shalulia had said during Sabaody? She wants her revenge on the Straw Hats, so he could be potentially sent to Mariejois by her request (she has power over Marine rulings). Oda also isn't the type of person to leave plot threads like that I'd like to think, and I don't see how she can ever do anything without meeting Luffy, which would probably be at Mariejois. I also don't see how you solve the whole Tenryuubito problem without the main character of the manga being present, and its not like they will just up and leave the holy land.
So while all of this is going on, the Reverie is literally happening at the worst time. Every Kingdom that take part in it, including Drum, Alabasta, Dressrosa, and Fishman Island, and would have to decide on whether or not to side with the Straw Hats after they saved their countries in the past.
This is when, I think, the entire scope of the story of One Piece would change. The world literally plummets into revolution. This "War" probably won't be as big as the final one (as I definitely don't see the Yonko actually getting involved), but I can definitely see the Revolutionaries playing a huge part in gaining a large amount of countries to join their movement.
And this is also Vivi's opportunity to meet Luffy and the others again. Oda is planning something huge with her character, you can tell the way she was reintroduced. She did ask at the end of Alabasta that if she met them again, would they take her out to sea. Whether it revolves around her actually joining or not, I think her character will be used as the spark that will change the One Piece world forever. Her country is the first instance where a kingdom was saved by them. She also has the opportunity to finally reveal that it was pirates that saved her country, allowing other countries like Dressrosa, FI and Drum to stand up against the government with her. And with that maybe others will join.
That being said, I like to think of One Piece's story split into thirds. I think Ace's War was the end of Part 1, this "war" over Luffy and the ignition of a revolution that will end Part 2, and the Final War against all Yonkou, the Government, and for the Pirate Throne as Part 3.
Lastly, if anyone remembers, when the Straw Hat Fleet was formed, Oda forshadowed an incident happening with them. I believe it to be this, the incident/War that ends, in my eyes, Part 2, just like Ace's "incident" that was sparked after he fought Blackbeard and ended Part 1. This would show that his Grand Fleet is willing to take on the Government/Marines by themselves, further sparking other crews to join the fleet later on. Part 3/the Final War, is the culmination of everything ending and coming together in One Piece (FREEDOM, ONE PIECE, RAFTEL, VOID CENTURY, ect), which by that I mean that the Grand Fleet would probably only be a small factor in that, relative to every other thing that will happen then, which is why I don't think that that is the incident (plus, I doubt Oda would call the Grand End to his Magnum Opus, an "Incident"). I'm not sure if there would be another time skip at this point, but I think something major will happen this world change again before the "end" (When Part 3 begins).
I believe Luffy needs a struggle like this. The entire manga, he's been saving people selflessly, its time for others to do the same. In that essence, he becomes stronger, because he understands that not only was Roger immensely strong, but was also powerful because he was able to pull allies from seemingly nowhere, and that will lead to the world following Luffy's view of freedom. Luffy is the Living Will of everyone who has this dream. He embodies it completely, so what happens when that Living Will is captured and restrained?
Hopefully this doesn't sound too fanfic'ish. I remember when ace was fighting Blackbeard, I was daydreaming constantly about Luffy potentially having to go rescue him. I also was sad they hit the Red Line and never explored locations like Impel Down and Marineford. Then Oda graced us with one of the strongest storylines in manga, showing both and having several arcs dedicated to Luffy trying to do so. I am now currently sad that we have passed the New Marine HQ and Mariejois, yet both, like the Old Marine HQ, are currently shown as teasers to locations not yet visited, as if Oda is planning on showing them off later. This is also when we would see parts of the true nature of the Gorosei and find out bits and pieces to the Void Century (Raftel would explain the rest).
Tl;dr: One Piece is divided into 3 parts. The first was up to Ace's War, the second will culminate into a Luffy rescue arc/war that involves New Marine HQ, Mariejois and Tenryuubito, the Reverie, Old Kingdoms, and the Revolutionaries, revealing potentially stronger enemies (from the Government itself, such as Kong or the Gorosei) and bring that part to an emotional finish, then Part 3 starts the beginning of the end with the Final War, with the Yonko, World Government/Marines, the last few islands (Elbaf, Raftel, etc), and FREEDOM.
EDIT: I am also unsure how to factor in the destruction of Fishman Island into this. Maybe after rescuing Luffy, they all retreat there. Perhaps the beginning of Part 3 would be the destruction of that island prompting Noah to be used and bring all fishfolk to the surface.