Re: The Will of D
The theory sounds pretty sounds solid though I am more curious on how the WG found out about Buggy's connection with Roger all the years later. Like you said, the WG only pay attention to the top dogs and at the time Shanks and Buggy were apprentices. It can be presumed that they weren't on the Oro Jackson very long, possibly only during the last stretch so that would make their cover even that much more low key. I'm willing to assume there will be more talks of Roger and finer details on what happened to his crew after being disbanded and after Roger's death. Maybe there are other crew members that are still alive and possibly either are in cahoots with the government or maybe WG found them and forced the information out.
Since Raftel has only ever been reached by Roger, one can assume it is probably the most chaotic or hard as balls to reach islands in the New World. It is was probably too dangerous that only Roger and few of his elite crew members like Rayleigh could have made it there. I believe that Shanks and Buggy never stepped foot in Raftel but that isn't to say that Shanks and Buggy don't know what One Pece is.
Roger said that he "left" the greatest treasure in the world on that island. So it was found somewhere else presumably. Maybe where the One Piece was originally located is where the answer to what is the Will of D is. It also goes with saying that the Rio Ponyglyph might also be there and that is how we'll get the answer to what is the Will of D.
This brings me to my theory of how the Yonnkou became to be established, starting with Whitebeard. It has been revealed that he never had interest to become Pirate King or to obtain the One Piece, he just wanted a family. Roger told him about the Will of D and the fact that One Piece exists, he might even know the location. I want to believe that he's been protecting the One Piece all this time by fighting off the Marines and the WG. I mean, the closest power to face off Roger on equal footing was Whitebeard, you can't mean to tell me that the strongest person in the world isn't capable of obtaining the One Piece by now. It's been over twenty year since Roger's death. I also believe that for this same reason Shanks is also a Yonkou, to protect the location of One Piece and to guide Roger's spirit that lives on in Luffy back to the treasure.
So yeah, this theory of yours Dagoro has a lot of rational logic to it.
“Pirates are evil? The Marines are righteous? These terms have always changed throughout the course of history! Kids who have never seen peace and kids who have never seen war have different values! Those who stand at the top determine what's wrong and what's right! This very place is neutral ground! Justice will prevail, you say? But of course it will! Whoever wins this war becomes justice!”
― Donquixote Doflamingo