I don't think you realise how much the English clubs income comes from their television deals. There is no way they would risk it, & if they did what would be the repercussions. Presumably even the Super League would have some form of relegation, as would be soon stale with the same sides in it year after year. Now, this might not be so much a problem from the Spanish duo, Bayern, Italian clubs, & PSG, but there is no way the English sides would be welcome backed with open arms that's for sure. Say for instance Man City, Utd, Chelsea & Liverpool join & then one of them is relegated & replaced say by Spurs( due to the money) the Premiership & football league will hardly say welcome back lads, but tell them to rejoin the pyramid down say level 10. Love to see that, as long as it isn't us.
Unlike other major leagues, the English ones are riddled with clubs that were once big & have faded away. The championship is full of them. We even have two previous winners of the European cup amongst them. As big as the current top 5-6 are they could easily be replaced.