Or... someone could incorporate all that potential and make a new script, with new characters, new names, etc - so it doesn't reflect on the existing masterpiece if it goes wrong

The Godfather is a work of genius, but it's not the only time filmmakers ever got it right. If everyone had decided that the Godfather was the peak of cinematic achievement, so we should spend the rest of our lives only making Godfather-connected things, a) it would cheapen the Godfather currency, and b) we wouldn't have had Goodfellas, Casino, Scarface, Donnie Brasco, the Sopranos...

I agree, there could be a wonderful film made set in Sicily about the old-school Mafia before it moved to the US, but does it have to use existing characters?