I agree, Beren and Luthien would make a great movie.
But then comes Turnin Turumbar. Lots of material there. Especially with the resently printed more fleshed out Children of Hurin that Christopher Tolkien released. But is the general movie public ready for that one?
Turin married his sister. Granted, he didn't know who she was, but remember, these are the people who worried about The Two Towers because of 9/11.
Then he just goes from land to land. Always becoming a leader and urging open war. Only to get the city destroyed time and again. He just keeps trying until finally killing himself. This wasn't John Henry who beat the steam engine, but died from the work. This was a man with blood on his hands, lots of blood. Who finally plants his own sword through himself.
Taken as a part of the entire tapestry that is the war of the Jewels, the story was great. But as a separate movie, I don't know if it would play well with audiences. Maybe I'm wrong, but I don't know if Fantasy Action filmgoers are ready for that sort of Tradgedy.
To do those three, Beren, Turnin & Gondolin, you really have to go the whole nine yards and get Earendil to call upon the Valar. Without that, all these stories never overcome evil. I think you really need that ending. That and the special effects to show the Wrath of the Lord of the West, now that is a visual battle I would like to see atempted.