I was thinking about what the plot for Part 4 could be in the half that continues the story after Part III with Vincent as Don....

all successful film sagas always go in a new direction after a few films.

Perhaps in GF4, instead of the Family going against another one of the New York famalies and their Don, the Corleones will be involved in a war with the Russian Mafia or the Colombian Drug Mafia. I would like to see the Corleones kick the Russians ass or Colombians ass this time instead of another Italian family. Perhaps the Italian famalies would align against an outside mafia.