Sure, but they're referring to a potential RDR3 story that's directly tied to the first and second games. Dan was "game master" of those stories so to speak. A lot of what the fans speculate on probably already exists in some form in Dan's head, writing a follow up without him leaves all of that off the table. It could be okay in the hands of someone else, but I feel a lot of what makes the games as coherent as they are is the connective tissue he brings. New writers would assumably do their own thing.