I think they should leave it alone. III wasn't great, but it was decent and I would hate to see it watered down further. Sometimes you have to move on.

However, if the new novel by Winegardner is a hit, expect a movie version. Of course, they'll have to get younger actors to play the parts, but I think there will be more Godfather movies in the future. Whether or not they'll follow the storylines of the first three remains to be seen.