Maybe the won't forget much stuff, i mean dislike One Piece. But Oda didn't forget much, so it's possible that the devs of this game won't forget much either.
I didn't mean to literally to forget. When creating a new world from scratch, you are free to add any details you like. However, as the story goes, new characters and background are added, you will start getting restricted by what you have already made. That's why making something as big as One Piece would require very efficient management to take into account all of the details, otherwise you risk breaking your own rules or making any already existing characters meaningless and overthrown by the new ones. Such task requires a very experienced writer, or better a team of them, because despite how skilled you are, you simply can't keep everything in mind.
Having more writers might work better for GG production. It will spread the workload from one person to several and probably increase productivity. Also, having different writestyles will make the game more feel more diverse (if they are in perfect harmony of course, otherwise it will suck). Of course, it can't be a person per route, since there's too many of them, but having 3 or 4 to make new content and maybe even fix those years old errors and typos would be great.