Darth Revan. The Vintage Collection. Courtesy of Hasbro.
It’s impossible to consider yourself a fan of Old Republic content and not recognize Revan’s name. The Jedi-turned-Sith-turned Jedi was responsible for the Jedi Civil War, breaking away from the Order in favor of the power the dark side of the Force and leading a Sith army to defeat them.
According to Old Republic historians, Revan was the first known Jedi to “fall” to the dark side (these individuals were appropriately labeled “fallen Jedi”). Many, of course, would eventually follow suit, though you didn’t need to be a Jedi first to “fall” become a member of the Sith Order. Some, such as Darth Maul, were trained from birth in the ways of the dark side of the Force.
His story is unique since he was both a hero of the Sith and the Jedi at different points in his life. He started out in the Jedi Order, left it, and was saved by Bastila Shan, who eventually helped him conquer his former apprentice and weaken the Sith.
Revan eventually leaves everything behind (again) to embark on a mysterious quest in search of more information about the Sith. And that sounds like a pretty interesting premise for a trilogy if you think about it.
Overarching quest: Find out what Revan was trying to find out, with subplots galore. Everyone would be on the edge of their seat waiting for Revan to finally appear, which would pretty much be a dream come true for KOTOR fans.
Honestly, even just mentioning Revan would get some fans excited for future possibilities.