After seeing the leaked pictures of Adam Driver in X-Wing fighter gear, and knowing that Driver is supposedly a/the bad guy in the film, could it be possible that he is playing a young Soontir Fel in flashback scenes and a good portion of the movie takes place in flashbacks? These are all rumors, of course, but I've read one of the main characters is said to be a stormtrooper. There have also been rumors that one of the main characters will end up betraying people at the end of the movie. It's also been confirmed that there will be flashbacks in the movie, as Carrie Fischer's daughter is confirmed to be playing Leia in flashback scenes. Soontir Fel trained at the Academy with Han Solo, so it could make sense that he would be depicted in Rebel/rookie pilot flight gear. Fel was one of the most successful Imperial pilots (leading squadrons of stormtroopers) before secretly defecting to the Rebellion and being discovered later in his career, which could be seen as "one character betraying the other characters" if the movie centers around Fel's early life as a pilot and then progresses into him in present day 30 ABY. Could Driver be playing Fel, or a Fel-like character?
Sounds like a solid theory to me.