My idea is to do it like GF2.
With falshbacks: 1920-late 30's.
Prohibition, wacking the Mustache Pete's and how they grow. How Sonny made his bones, how Luca get involved and more. Also the bussines with Hyman Roth and Moe Green.

And new with Vincen: These days
Maybe he could have a piece in Yukos/Sibneft (big oil companys in Russia). These oilcompanys are not totally legitement(tax-evasion). Poetin attacked these oil-big-shots(exapmle: Chodorkovski). The preseidential elections come. Corleone owned newspapers, tv-channels. With a media-campagn(campagne)and things like that Corleone and partners (Chodorkovski, Abramovich)convice the public and there friend (......maybe Chodorkovski himself) became president. He minds his own bussines.

i'm not sure of this (the last thing in Russia) is possible. Maybe there is something that could'nt happen.