Companies like Prada will never have the leverage to do anything.NY is a really big market to have to stay out of. I think your solution is a practical solution on a certain scale. But when things reach the scale where it becomes a proposition of "take it or leave it", where leaving it is more costly than taking it. They do the thing that costs less. It's sort of using Capitalism's shortcomings against it to have power over these companies to get them to capitulate.
So when things become of the scale of NY, probably only way to defeat it is for an association of merchants to all leave. But it takes nearly all of them to do it in a way that hurts NY enough to pressure them to stop. And that's hard to do.
It wouldn't take all companies to abandon them, just some really big important ones, for instance Procter Gamble or Pepsi. Things that regular people would miss right away. They could run ads on TV telling the people that they had to pull out because the government there is bat**** crazy, and they can not do business under the current law.