Dude, the reasons you gave for Shanks and Blackbeard being on Elbaf are weak, hell Shanks leaving Elbaf right before Luffy's arrival is already an indicator that he won't meet up with Luffy there.
And as others have said, there are too many sides at the same time. Oda should separate the confrontation with the pirates and the WG&Marine.
In my opinion, given that Luffy is already facing the World Government in Egghead and that Elbaf has a strong relationship with the revolutionaries and the Poneglyphics, I think it will be a saga dedicated exclusively to WG&Marine
Since you clearly didnt fully read my post above nor the OP, let me repeat myself more clearly:
- I never said Shanks and Blackbeard's points for being on Elbaf are strong, all of this RIDES on where the Burned Scar Man and 4th Poneglyph will be. The only thing I said was clearly Shanks has ties to Elbaf, so if all of this occurs on Elbaf then it supports the other Yonko being there. Thats the point in the OP being made, along with the fact that Oda has a tendancy to combine shit to resolve it. He himself is hyping a huge conflict, not me.
- Case for the above is if they arent on Elbaf, then they'll (Burned Scar Man) just be in their own territory after, which doesnt erase what Im talking about, just removes the aspect of it being Elbaf.
- I already separated the conflict with the RA/WG from this point. We are already seeing a very clear line separating the Marines and WG. This much is clear. Nothing states the Marines will be involved with the WG fight directly.
- Finally things being fully separate doesnt really track with Oda's MO, otherwise he wouldn't have had Ryokugyuu say they (the Marines) are going to fight the Yonko eventually. He wouldnt have had Kuzan join Blackbeard or capture Garp. This all straight up involves the Marines in the Yonko conflict.
Tldr: Replace the OP title with "X Island that includes the 4th Poneglyph will be OPs longest arc" instead of Elbaf, my point remains that all of these relationships are still there.