Diablo is getting a board game and tabletop RPG that will “continue the lore and story” of the video games
(www.rockpapershotgun.com)
In a world where there's the system The One Ring, I don't see a point in doing any other Middle Earth system. Perfection has already been achieved (for this specific setting).
Concerning high-level play, I think having way lower HP for everybody would also fix a lot of things, since the main issue is that battles take forever due to having to whittle down ridiculous HP sponges.