“The Hunt for Gollum” isn’t a terrible LoTR spin-off idea. That said, if I could have any part of the legendarium adapted by Peter Jackson, it’d be the story of Fingolfin and the Silmarils. “Thus he came alone to Angband's gates, and he sounded his horn, and smote once more upon the brazen doors, and challenged Morgoth to come forth to single combat. And Morgoth came.”