2 storylines the first one in the 1930's showing the corleones rise to power and the 5 families rise to power and young sonny,tom and fredo getting into the family business and gencos role as the consigliere and clemenza and tessio becoming capo's also pentangeli and hyman roth could be involved

the second storline could be set in the 80's with vincent running the family business into the ground because of drugs and tries to get a reluctant michael to help him out

the only way this would be succesful is if de niro was vito, andy garcia was vincent, pacino was michael and possibly scott caan as young sonny and karvey keitel as a younger pentangeli and francis ford coppola as director