This sounds like a very bad idea and I'm sure that Mark will probablly write the screenplay but here are some good ideas.

1. You could take what Puzo has already written about Godfather 4 and let Coopola work from that.

2. You could have a movie where you show what's happening to Vincent in the present after being the Don for 20 some years and also have some flashbacks to the rise of the young Vito Corleone as he could still be played by Robert DeNiro and there is enough unused material in the origional Novel to make a good story. You could also have Vincent being advised by present Day Micheal before he died and maybe even show Mary's funeral as a starting point.

Pippi