I agree that if GFIV does come into development that the story should definitely revolve around the character of Sonny. I have always been fascinated by Sonny and feel his influence on the Corleone family was undermined in the previous movies, but hinted at by the fact that they made his illigitimate son the new Godfater in GFIII. However, we must remember that if they do a story about him, they will have to reflect up until he died which means it will come across the same time as the first movie. When that happens they will have to use different characters to play michael, fredo, vito, etc. and I dont know how well any of us will be able to take that.