Earendil, I always found his story interesting.
Beren and Luthien.
Yep, I agree there! Would love to see an adaptation for these two, plus the children of Hurin!
I think, if Amazon Prime wanted to produce a direct-to-video animated movie to promote their upcoming series, I'd like to see an adaptation of "The Tale of Aragorn and Arwen" from LotR Appendix A. However, the story of Elrond & Elros might be more appropriate for setting up the show.
I think I might lean towards the war in the north, a lot of the actors could technically still make cameos (if appropriate) because of their ages, and it is such a great unexplored area!
Obviously I would love to see other ages as well, but because of the timing right now, I would probably go more for that :)
The New Shadow?
The children of huirin. Can't for the life of me think who to cast for tuition though. I'd love to see the dragon helm of for lomin depicted in a movie