How about the revenge factor? Vincent & Michael don't lash out at SOMEBODY for Mary's death? C'mon.
And how does the Kay/Michael/Anthony relationship change with Mary's death?
And what happens to the deal for control of the Immobiliere?
The fall of the Soviet Union/the rise of the internet/the rise of religious extremism/

Connie's role/death.
What does Vincent become?

And the flashback potiental- Michael;or DeNiro as the Don 1935-1945 in NYC;the Luca Brasi story;Sonny Fredo Michael & Connie as kids/teens...

the possibilites are there...