No one has mentioned the most important aspect of this great idea...who would be cast as Vito and the three sons during the 1930-45 period. The only obvious choice I can think of is Lance Bass of N'Sync as an adolescent Sonny.

Seriously, who among today's actors could bridge the gap between Vito at age 35 and age 50ish? (Excluding DeNiro: I can't see him reprising his breakthrough role)