I mean, a school could just disaffiliate from the NCAA. They could run independent sports programs and play other independent schools, or join the NAIA or some other association, or start a new association. They won't though, because ultimately it's all about the money.

Also to your point about enforcement, you'll see that the money-making programs (i.e. Football and Basketball) at the big D1 schools get away with a lot more operating in the gray area than small schools and non-revenue sports. The NCAA isn't going to shit in their gravy train. They save the virtue-signal enforcement for schools and sports that don't make any money anyway.