There’s no need for any sprawling mythology to painstakingly explain every aspect of its existence, but there are literally thousands of years in the Star Wars timeline that have barely been covered in any form of media so far.
In fact, the beginnings of the Sith were only officially added to canon last year, but we’ve nonetheless heard from our sources – the same ones who told us Ahsoka Tano would be making a cameo appearance in season 2 of The Mandalorian long before Rosario Dawson’s casting was confirmed – that the most evil outfit in a galaxy far, far away could be getting a live-action origin story of their own.
The Star Wars Book was released last October and offered the broad strokes of the nefarious Order’s formation, which tied up a few loose ends from the expanded universe. In short, it was confirmed that the Sith were founded by a splinter group of Jedi who discovered pure power can be attained and harnessed by devotion to the Dark Side of the Force, and it’s hate and rage poured into kyber crystals that give their ligthsabers a red blade.
The Sith’s homeworld of Korriban was recently reinstated as official canon as well after briefly being rebranded as Moraband, so there’s even a location in place for the majority of the action to unfold. Indeed, a feature film set at the very beginning of Star Wars focusing on a rogue group of Jedi turning their backs on their oath and forming the Sith has plenty of potential, even if you could make the argument that not every single part of the intricate lore has to be explained in painstaking detail. Still, it would at least be a fresh and interesting approach to the material.