US analogy: imagine that Texas said you didn&#x27;t have to pay Federal income tax. After a couple of years of wrangling, this gets ruled unconstitutional. Would you expect to have to pay the back taxes?<p>(it doesn&#x27;t quite map across directly, because EU federalism is less central than US federalism; in particular the EU has no direct tax powers, and we haven&#x27;t had the Federalism civil war yet)