They still don't have the rights to The Silmarillion. Just Hobbit and Lord of the Rings plus appendices, just like Amazon. Supposedly they are not trying to remake the Hobbit or Lord of the Rings, so could be more ancient history mentioned in appendices, or could be more recent history like the animated movie coming out next year "War of the Rohirrim".
Peter Jackson is in the loop, so could be involved. If he wanted to do something tied to his other movies, he could do a "War in the North" movie that covers the unseen events that happened at the same time as Lord of the Rings, and could include some characters and sets used in both the Hobbit movies and Lord of the Rings movies.