4. Crimson Dawn Maul
Yes, there are plenty of stories about Maul, but the same argument applies to Ahsoka, too, when she got her season for Tales of the Jedi. Most of Maul’s life has been covered except for one particular part, which is his time as the leader of Crimson Dawn.
The Clone Wars Season 7 was the earliest indication that he played all sides by pitting his own collectives against each other. Crimson Dawn came out on top as it’s still around during the time of Solo: A Star Wars Story. There are a few details about Maul from that time that we’ve gotten from Qi’ra during The War of the Bounty Hunters and Crimson Reign comics, along with the novel Crimson Climb, which is exactly the story I want to see onscreen.
Maul told Qi’ra everything about the Sith. He taught her how to hold her own against Darth Vader, where to find artifacts to defeat Emperor Palpatine, and essentially took her on as an apprentice. That’s an interesting relationship waiting to be explored. What kind of trust or fear is built for Qi’ra to take on this task for Maul after his demise to the point where she outlived all the Sith she was trained to beat?
Even before Qi’ra’s rise, anything about Maul's time in Crimson Dawn is scarce in this time other than the point he was alive and working in the shadows. Tales could even explain how and why Maul arrived on Malachor for the events of Star Wars Rebels Season 2. There are still plenty of stories to be told with Maul for fans to enjoy.