If you have fiscal cooperation, a single currency, a governmental body that forces regulations and laws to its member states and in the end even a unified army (which I think will happen in the future, especially since the US is taking more and more of an isolationist approach to foreign policy) isn't that closer to a federation than it is to a simple trade union? Not all federations need to be a massive nationstate which in Europe would be impossible by definition since you can't create a new nation out of thin air in a few years when you have nations that have existed since the time the concept of a nation was created.