Outside idea. Stop trying to copy the NFL or NBA. Try multiple leagues (like college conferences). Europe has 700+ million people. This feeds all the main euro leagues and ultimately the champions league. Teams are very local. Large population centers can have multiple teams. Us has 350 million, North America has 650 Million.
What if there was a west coast, east coast, midwest, and southern leagues. Dallas and Houston could have multiple teams. Austin, SA, El Paso, etc could have teams. These midsize cities that don't have major pro sports would provide a a good base of support. This would make relegation much more palatable. Allowing the big teams in the big cities to pay their way to the top if desired. Player transfer system now becomes possible, with real $$ incentive to develop players.
Then a champions league like event every year. Could eventually include leagues in Mexico, Canada, etc.
I know. Will never happen.