Well id say Apple is set in his belief and wont be persuaded. Im new to this board but i know alot obout these movies and the book and I think it would be easily possible to make a good sequel better than 3 id wager.
There are plenty of plots and stories that didnt make the screen, Id like to see a young Luca Brasi just under the employ of the don, the stories that shape Clemenza,Tessio and Al Neri. Also the future after 3 needs to be explored somewhat. Michael need not be a main character and the future of the family in a modern world would be intriging. You all act as if Puzo thought this all up from scratch and he did not. The stories of the real mafia are the basis for most events in the book and films and Im sure there are plenty more that could be reworked. There is twenty years of the mafia that could be explored in a part 4. Some of the families are named after new men and why this is, the rise and fall of John Gotti and the preceding war, the banker and industrialist don such as castellano being murdered for his progressive thinking, the turning of a families underboss and exposure of the omerta ceremony and popularization of the mafia all could be dealt with within the context of the Corleone family and I think with the correct writers be very enjoyable and by the way I doubt there will be a movie of the new books also but apple is dead wrong here, I doubt if the author has the rights to the film or if film rights would even be offered to the publishor. This is common when writing in a franchise, Such as Star Wars the Timothy Zahn novels had enourmous film interest but Lucas made sure in negoitiating that no film rights were even discussed and they will never be available except to Lucas himself and im sure Puzo's estate as the same assurances
Just to show you what you believe is not law apple