If we want this to be a universe based off of the current timeline, we'd have to explain what happened to the straw hats. I'd hate to say they failed to find One Piece or were captured or something like that; I love the guys too much for that. Maybe Luffy becomes the next Gol D Roger and turns himself in after enjoying his term as the king. Either that, or the straw hats mysteriously vanished, and rumor has it that they are protecting the One Piece. Essentially, if we go canon universe, I'd like to effectively deify the Straw Hats in some way.