Before the prequels were released, I envisioned a lot more of Vader hunting down Jedi. Now that we have Anakin’s backstory, I’m not sure a movie with Vader as the central character would fit well. I think instead you would have to make something centered around a group of Jedi who survived Order 66 and are being hunted by Vader. Focus on and build those characters, then let Vader do what he does best, be the menacing villain who inspires fear. That sounds a lot like Rogue One with more Jedi, so maybe that wouldn’t fit well either.
Perhaps Vader best left to surprise cameos that leave us wanting more.
A ‘Jedi Purge’ movie would be sweet in that it would probably be the last ‘big’ unexplored issue of what happened between ROTS and SW’77 that would be of interest to main audiences? Chris Nolan doing it would likely bring a new spin or approach to how it could be done or filmed.
Though like you, I’d prefer minimal-to-cameo Vader being involved or seen.
Bounty hunters for sure, crime lords, defectors and doule-agents, and some of the characters from Solo & Rogue One in differing and new environments as well. The seeds or birth of the Rebellion as it were. Frightened or oppresssed every-day folk too scared to help the few remaining Jedi in hiding - or those having no choice to get involved on behalf of the Empire…