It's nice theory, but I can only see that happening where you have a large number of strong players tryout for the team year after year. A coach can then make an "in house rule" to where only Seniors and Juniors make Varsity unless there aren't enough to go around. If you have a program that has been struggling or is not an Irmo or Wando, then I doubt the coach will do that if he has some strong young players to pick from.
