But the US states are just that, whereas most states in Europe are NATION-states. Nice idea, but use with caution.
"A nation is a society united by delusions about its ancestry and by common hatred of its neighbors." - William Ralph Inge
France has Bretons and Basques, it's almost too late at night to get started on Belgium, the list goes on. Let's reduce Europe to states. If the aforementioned regions want autonomy let them operate (and be represented) independently within a Federal EU. If they've a different way of doing things re:taxation or social policies they should be given the freedom to do so, but they shouldn't be given freedom only to be allowed to degrade into ultra-nationalist backwaters, we do need to be very careful about that.