He wasn't able to say much, but he did give a little hint about Finn's role in the film, and what made the character interesting to the actor.
"I think I'm always interested in characters that start off one way and end another. I find it very boring to have to read a script where the character always knows what to do, knows who they are, has a blueprint for their lives. I just feel that sort of character is painted for a perfect story. What has always interested me, and what has interested a lot of people, are the characters that are unlikely. The characters that don't necessarily fit or match the status quo," Boyega said. He continued, "Finn isn't a guy you would expect to be involved in this story. The fact that he's a Stormtrooper. We don't [usually] go into [Stormtroopers'] pasts or lives much: how the dynamics work for them, how they were recruited — we don't ever really see much about the past there. It was interesting to me to have that kind of character."
Boyega also addressed signing on, saying he's "all about story." He said he doesn't think, or at least didn't before signing on, about what affect the movie could have on his career. "For me, it's just all about making sure that this is a really cool film. That [Finn] the best character I can make him. As an actor I wanted to do a great, great piece. As a fan as well."
And a fan he is - the actor kept six lightsabers, and has them in his home. He plans to give some of them away to "certain people," likely close friends and family, but one is around to "swing around a few seconds when I walk around the house." We all do it, John, don't worry.