The best chance for a non-SEC team to win it will be for an SEC team not to make it because of their tough schedule. The next best chance would be a team that relies on Defense and special teams, and therefore has a slim margin of error, to make it from the SEC (basically UF last year). But it's hard for a team like that to make it through the SEC. Even when we have teams that rely on their D like Bama and LSU, they generally have a pretty solid ground and pound offense.
Once the playoff system starts, if the SEC remains like it has, it will be very hard for non-SEC teams to win, unless they set up the rules so that conferences can only send one team to the playoffs. I think Alabama or A&M would have been favored to reach the finals if you put them in a 4 team playoff last year, and Florida or Georgia would have been good enough to, although probably not favored.