I like the train of thought but why don't we have 5s play 8s and 6s play 7s and the loser is relegated. That way the only way you won't be relegated is finish in the the Top 4.
We had an extreme case last season, as both teams from the same conf lost the play down. Moreover the new team being demoted from the stronger division, gave up the game and is now a bot . The result is that one conference get 4 new teams, 1 bot and three from the lower division. The other conference is significantly stronger, having the favourite for the final two seasons in a row but failing to promote because of injuries.