I don't think BYU will ever become a consistently elite (top 10-15 ranked year after year) program. We will never get the depth that other top programs can get. We will get get elite individual players but we just can't compete with the depth that others have and because football is such a violent sport, we can't rely on the first string players to carry the load for 12 games to make some noise. There will be injuries to top players and we don't have the talent at the next level down.
It would take a perfect storm of players, coaches, and luck to pull off an undefeated season and that is just unlikely to ever happen.