I think, for Oda, Elbaf needs to be the threshold where all of the final mysteries centered around other characters not directly in the endgame needs to come to play. Unless theres more islands after it but before Lodestar, then it needs to be addressed here:
- If Scopper is a character Oda means to reveal, then he should be revealed here ultimately. If he's the person drinking with Crocus, then thats a 500 chapter mystery resolved.
- The Burned Scar Man is a mystery that should also be addressed here. Assuming this silhouetted person isnt him, then Scopper/this person can possibility give more detail on who the BSM actually is in Elbaf. We need the 4th RP to continue the story, otherwise getting to Lodestar means we cannot advance past it to Laugh Tale.
- Shanks, Blackbeard, CG, Akainu and Imu all need to make their final moves during this arc (again, assuming this is it). If Shanks is heading out to attack Luffy's fleet, it needs to happen now. If Blackbeard hears about the Ancient Weapons, then he should be going to Wano in the least (I doubt he'll get Shirahoshi in time, but she might play her role in the endgame anyway). If CG is meant to to recruit more people, it needs to happen now as well. Akainu needs to mobilize and leave New Marineford. Imu depends on where the WG will get involved.
- Possibly an extension to CG, If Oda plans on having former Shichibukai involved in the endgame, whatever needs to happen at Impel Down with Magellan, Bon Clay, Doflamingo etc, needs to happen very soon. Hancock needs to move out, whomever rescues Weevil also needs to play their part.
- Any mysteries we have left on the Underworld, Cloning, etc should all come from Stussy. I still think she'll end up on the Elbaf ship in the next chapter or two. She's the gateway into understanding those things and Rocks.
- There are allegedly, a bunch of Impel Down Level 6 escapees still at large. We were told in DR that they all congregated somewhere, but that was it. Could this be how CG gains power? Could they be in Warland?
- Any lingering plot with Big Mom probably needs to be wrapped up here, with or without her presence.
- Urouge is still the last elusive SN not tied to any arc plot. Its gotta be here, either some designated Sky Island portion/lore of Elbaf or something close.
The list goes on, but this is the relative gist of it. Elbaf either needs to be this massive conglomeration of plotlines, or we are still stuck at square one for many of these heading into the final conflicts, again, assuming Elbaf is the last island before everyone starts to fight over the 4 RPs.