It’s almost certainly too big, sprawling/disconnected and thematically diverse to ever all be filmed. But if it were, or if your favorite part of it were filmed, who do you envision in the various roles?
Just off the top of my head:
Morgoth: Ian McShane, Deadwood
Sauron: Jude Law, Sherlock Holmes
Luthien: Keira Knightley, Pride & Prejudice
Beren: Jeremy Renner, The Hurt Locker
Turgon: Daniel Craig, Casino Royale
Feanor: Ciaran Hinds, Munich
I believe the work goes public domain 70 years after the death of the author-since Christopher Tolkien is still around, said film could be made no earlier than 2082.
I don’t think that the creation saga would be done justice by actors. You could make an abstract anime about it, though.
Same thing goes for the War of Wrath (except less abstract.) Great animation opportunities there, and done in an anime style it would be great to see elves’ eyes literally glowing with the light of the West.