You have to love the internet sometimes. Take a look at actor Diego Luna (Cassanova) in the Star Wars: Rogue One promo image that was released over the weekend. His casting has gotten a few folks trying to connect some dots.
So what is the theory? Well, take a closer look at Luna in the image… does he remind you of anyone? Maybe someone from an earlier Star Wars film?
Do you think he looks a bit like Luke Skywalker's best friend from Tatooine, Biggs Darklighter?
Well, that's what a lot of people are starting to think. Biggs left Tatooine to join the rebels just prior to Luke leaving on the Millennium Falcon. So the timing is off… except the only reason we know when Biggs left is based on the deleted scenes from Star Wars: A New Hope. Whether those seasons are considered canon isn't clear. So it is possible that Biggs could have been part of the rebel team that stole the plans for the Death Star. And it would make sense for Disney / Lucasfilms to want a character that fans are at least a tiny bit familiar with in the first spinoff film.
This theory may simply be based on the looks of the character… but it's starting to gain some traction and in the following interview, Luna dances around the questions when the interviewer asks him straight out twice if he is playing Biggs but does not answer. Check out at around the 3:25 mark…