If the EU actually made US citizens apply for a 'proper visa', you know it'd just kill the VWP on the other side as well. There would be retaliation with 100% certainty.
I don't think it'd be that popular anymore at that point in the core EU countries. Let's just say the sentiments regarding Bulgarians and Romanians among the populations in the 'old' EU are at best a mixed bag. It'd be a tough sell for the Irish or Austrians that they can't visit the US easily anymore because it's policy that the East Balkans folks must be allowed to go to the U.S. without any checks in place. Allowing citizens from those countries without checks into the rest of Europe was controversial enough with people.
Now for that and many other reasons, I don't expect much to happen here.