I don't consider Micheal to be the godfather. And Vincent never was nor will he ever be Godfather. Vito was the Godfather Micheal and Vincent were Dons. The Godfather and The Godfather Part 2, were about Vito, even though Mike was a BIG part in the first two. FFC and Puzo think the same way, GF3 wasn't Godfather because Vito was the godfather, and since Vito wasn't in it it wasn't godfather, they wanted it to be Death of Micheal Corleone. A later-on-in-life spinoff. Vincent never even MET the Godfather. So he has nothing to do with Godfather.

I think a spin-off would be cool tho. Did puzo actually write a GF4 script?