The problem is getting the acting talent that would be necessary to play a young Sonny and a younger Vito. Some people have suggested Nic Cage but that would possibly be the worst thing ever, well with the exception of Leo Di Caprio as Sonny's son.

I would love to see more of Sonny and Luca Brasi. A great scene for any prequel would be Don Corleone dealing with the men Al Capone sends to New York. Since Mario Puzo died however the chances of a finished script being produced are slim.