If, the 4th installment in the Godfather saga could be produced to the same high production values and casting values of I & II, then #IV would be worth making, and worth seeing, and would be a compliment the others.

But what are the obvious pitfalls to making another installment now:

1. The level of graphic gore is rising on television. It seems there's this competition to see who can be the first network to splatter the most blood. There's a real art to showing violence without so grossing or shocking your audience that it detracts from the movie-going experience.
With the current trend, how can a "gangster" film not "go for the gore"? ? ? Just look at the progression from the excellent 5-Star thriller SILENCE OF THE LAMBS tumbling down to it's sequel HANNIBAL, a "hip" and "trendy" gore-fest that is but merely a 2-Star outing. Who can hold the line against these powerful market forces ? ? ?
2. Casting. If we follow the example of what we got with III, then whomever won't come back onboard is speedily written out of the story, no matter how helpful they would have been to the overall telling of the saga. And then, when others not so important say "Hey, I'm available", well then they're written in to the story, when maybe they shouldn't be there at all. Yeah, that's what I see happening, all over again.
3. I think it would take a miracle to get it right now. The Studios aren't committed to making any real Classics anymore. "Just make it with OUR values......and we'll milk it for all it's worth.....fist in the theaters, then pay-per-view, then cable. Oh, we've got those DVD releases down to an art now, what with all the SE, Director's Cut and Box sets available! !"
Yeah, there's the real "art" in Holywood these days -- Marketing clunkers, for all they're worth ! !