It should be CGI. Al Pacino is getting very old these days and should lend his voice and likeness to a CGI sequel. Or there should be a CGI movie or a miniseries or TV show taking place between Part II and III like I saw some suggestions on the forum. Or you could have a CGI movie based on the sequel books. If anyone were to touch The Godfather series it should be CGI therefore it would decrease the chances of it being a complete disaster for the entire series. My personal opinion is that no one should touch The Godfather series unless it could be guaranteed that it won't be a disaster.