I think this would kill off game as you are penalising managers for being successful or for being around for a long time. While encouraging newcomers is commendable penalising experienced players and forcing them to leave their current leagues is not the answer.
Kevin Bissell’s idea of doing away with tiers and have one league with classes within it fighting for class titles is better (or have 2 leagues with classes within). Of course just my opinion like yours.
If the managers follow the rules (no more than three top teams in the elite), no one gets hurt. Teams that have reached level 20 (or 30 after updates) can move to a league with less than three tops. Or even create their own league.
Three tops are fighting for titles and high scores from 1st to 6th places. Others are fighting for a place under the sun from 7th to 10th place. The number of new leagues will increase. But the number of active players will also increase many times over. Because each newcomer to the Elite will have chances for a successful performance, stable scoring, fulfillment of sponsors' tasks and quick progress of the team.
In Elite today, even managers from levels 16 to 18 mostly play the role of spectators. Many of them, tired of swallowing the dust of tops, simply abandon the game. While others find half-empty leagues in order to be successful at least somewhere.
This is nonsense. Every manager has the right to succeed in active leagues, even in the Elite. Otherwise, there is no point in wasting precious time and nerve cells.