Let them form their breakaway, tell them they are no longer part of their associations, UEFA, FIFA and their players are no longer considered eligible to play for their nations.
Will soon discover who would be happy to fund their league and existence and their only draw is playing highly uncompetitive football for a trophy that has zero prestige.
The division of the sport might end up like Olympic boxing vs pro boxing, one set of pros gets average money, plays in national leagues and world cups while another set gets mega money in the superleague.
Or the spilt between rugby Union and League, with differences in the rulebook. FFP wouldn't exist, nothing to stop them all hoarding up a squad of 30 top players.
You can't really stop out of contract players from moving to super league, yet if they run down their contract with eg barca and have no other options would they remain barred from the classic system?
On another note it sounds similar to the invite only club world cup, it guaranteed the same set of clubs a number of years in the competition.
The likes of Milan are a bit behind now, but with the amount of money they'd earn, it's enough to rebuild soon enough and leave Inter behind.
The 20 year membership is too long, it might be a starting gambit - a 5 year period would make it more interesting.
The EPL breakaway wasn't the same situation, we kept the pyramid system in place.