Ben Barnes seems like the classic example of a good actor who's never really had the material that suits him best. You know why Emma Stone dyed her naturally blond hair red? Because as a blonde, she was constantly being brought in for cheerleaders and sorority sisters and never getting the role, because although she looked right physically, she had a totally different vibe as an actor. That's sort of what Ben Barnes is like. He gets all of the generic leading man roles because he's classically handsome, but he has a slightly quirky sensibility that makes him seem like he might be better served by something a little bit more character-y. To this end, Newt Scamander would be a perfect fit. It's the lead character in a major blockbuster franchise, so it sort of goes without saying that they'll be looking for someone good-looking, but at the same time, Newt is a hippie wizard outcast, so he's not exactly a conventional leading man. Sure, it's taking a little bit of a chance, but one that has the potential to pay dividends if done right.