4. Qui-Gon Jinn
Once again I'm not sure how much Qui-Gon fits into the universe beyond the prequel trilogy, but I think an origin film could possibly work. He's often described in Episode I as being headstrong, defiant and so on, with a reputation among the council so an origin story could use this as its focus, showing the events and actions that led to the character getting this reputation despite being seen as worthy of being a Jedi master. His earlier days studying under Count Dooku or the beginning of Obi-Wan's training could also make a good story for the film. My only concern would be that Qui-Gon might not be a strong enough character to be able to carry an origin film by himself as the central focus, particularly since we didn't see very much of him on his own throughout the saga. A better option could be to have an Obi-Wan origin story showing his early days of training before the Phantom Menace that features Qui-Gon more centrally. However capitalising on Liam Neeson's recent revival as a badass action hero could also make an origin film work in Qui-Gon's favour.