This is my "Theory" on how Bungie ,if they put the other four spartans in the game, will do it. The main thing holding them back, at least what the people in the forums think, is that not enough halo fans have read the books. So how do you introduce these new spartans not out of the blue you ask? Easy, make a movie! Which they are doing. So yea I was just thinking about this and that would make sense since the movie is supposedly about the cheifs past. Im new ,this is my first post, so sorry for any repeated posts, grammar mistakes, and/or spelling mistakes.