I think it can be filmed but it should be a long movie. I hate it when Hollywood ignores major points in the book for time and money's sake.
Or when they concoct something because they think it works:
I remember the 2000 version where Meyer Wolfsheim tells Nick that he met Gatsby aboard Dan Cody's yacht. Untrue to the book.
Daisy messing up Gatz' name and calling him Gatsby, and having him just agree to be called that by her. They should have flashed back to Gatsby rowing out to Cody's yacht as a young man...hit that side story for a minute, and then bring us back. I'd really like to lose myself in the movie like I do the book.
Stick to the book. Of course, I realize that they want to make a movie that people besides English majors will see.
For casting, I think Dicaprio can pull it off. He did well as Howard Hughes. I also think Toby McGuire can play the meek Nick Carraway. I'd read rumors about Affleck playing Tom Buchanan. I think it would work. Interesting to see who they cast for Wolfsheim....Pacino? De Niro? They'd be good, but too expensive.