I'm not so sure promotion/relegation would work in high school soccer anyway.
Would you just promote the champion? top 2?
Things can change so quickly in high school soccer with the turn over in players that a team that does well one year, might not be good the next.
Plus it could be a travel nightmare.
Take 3A girls last year. BE won so they move up. That puts them in a region with Hilton Head, Bluffton, Colleton County and Beaufort. That is a horrible travel schedule.