Probably not an option now since Pacino and Duvall are now older then the characters at this age, and this was probably never an option for Coppola or Puzo, but I personally would be very interested in seeing how Michael and Tom made the push into legitimate enterprise, detailing how Michael is the successful businessman at the start of Part III. The film could climax with Tom's death, (by natural causes or otherwise ), and there could be flashbacks contrasting how Vito and Sonny became successful in The Family business in the 30s, with Michael and Tom becoming successful in the late 60s/early 70s.