The Jedi Purge is (or can be) a big subject. A bounty hunters movie set between ROTS and ANH that follows the extermination of the Jedi could be good. For that matter, any kind of bounty hunter movie might be cool, Fett or not. No reason to think the Empire wouldn't pay bounty hunters to keep an eye out for Jedi, after all.

I may be a lone wolf (esp on this forum) but I think an Episode 0 prequel that shows the first Sith/Jedi war and how the Jedi came to be associated with the Republic could make a cool movie too.

A Qui-Gon and young Obi-Wan movie might be fun too. It could tell the story of how Obi-Wan came to be Qui-Gon's apprentice. Or not, it could also be something else. Same goes for a Yoda/Dooku movie.