Euro is a common currency in the European Union organization. so it should not be one of the common currencies because it is not based on any indicator to evaluate the strength of that currency. I think when the USD weakens, it will continue to return to the gold standard era. This has happened and it will continue because people have a habit of repeating history. so that's my guess if the US dollar really can no longer afford to be the world's oldest brother, Gold will continue to take the throne.