1. The Great Sith War. An epic that takes place 1000 years before Episode 1. It can be filled with mythology that plants seeds for the "Skywalker" storyline. Tell me how the Jedi Order we know in Episode 1 came into being, the galaxy's discovery of the Force. What is the Sith's motivation? I want to know more about the dark side and the origin of the Rule of 2.
2. Bounty Hunters movie starring Boba Fett. The plot would involve hunting down a simple bounty, but it turns out to be something much greater - either a conspiracy or trap set to take Boba out of the game. Events from the main episodes can be alluded to as "easter eggs" but I don't want this movie to impact the mythology in any way. No need to shed light on any backstory, no cameos from the main cast (especially no recasting of famous roles), just give me a fast-paced action crime thriller. I think a good time setting would be between 3 and 4. The ending would shed light onto why Fett is the most feared bounty hunter in the galaxy.
3. I really like the idea of a gritty special forces-type movie (like Rogue One) but taking place between VI and VII. I think there could be a lot of unique action with the focus on the cost of war, particularly in the aftermath of the Battle of Endor.