If Neville was the 'Wrong Boy Who Lived', it would bring a whole new perspective. His relationships with his friends, teachers, and enemies might all be different. The story could focus more on his inner strength and hidden talents that were overlooked before.
Well, if Neville was the 'Wrong Boy Who Lived', the entire magical world's perception of heroes and chosen ones would shift. It would also change how his character develops and how he interacts with others.