True, as far as it goes. But I can't see the Euro or any other fiat doing better than the US. After all, when push comes to shove geopolitically, only the US is in a position to do any sustained shoving.
Some smaller currencies, such as the swissy or canuck might do better, but these are small markets that cannot possibly absorb the amount of buying interest that will be sparked by a continuing slide in the dollar, say below 80 on the index.
That said, diversification is always a wise plan.
That's why I only have about 30% outside the dollar.