Long term, I think the traveling part is pretty nonsense. The reason is simple - as more people start to pay with cards instead of cash the problem goes away by

Long term, I think the traveling part is pretty nonsense. The reason is simple - as more people start to pay with cards instead of cash the problem goes away by itself. Not having to carry cash at all is a better solution than only having to carry a single kind of cash. As for worrying about banks and exchange rates - if that is a problem I suggest doing something similar to how roaming charges have been regulated. That will probably be necessary in the long term anyhow as a precondition for creating a single market for financial services.