Would it be constitutional?
The United States do have a weird legal system, but it also feels a bit weird for one state to void contractual conditions imposed by Apple on app makers in every other state, in fact that I know in every other country. The words interstate commerce come to mind, and it definitely feels like something that is the remit of the federal government.
Come to think of it, how come not a single country has come forward with such a law already? Surely Apple cannot buy off all of them?