How about Cryptocurrency causing a disruption? Right now it is insignificant, but the growth rate shows that it can considerably affect the dollar in the future. Already countries with economic collapse are adopting cryptocurrency. Eventually weak fiat currencies will be replaced with cryptocurrency and those weak fiat currencies will go down like dominos. In the interim, there will be a need to have physical cash. So strong currencies like US dollar, Euro, etc. will have a temporary boost in value. Eventually that will get wiped out by cryptocurrency becoming dominant in scale. Eventually the FED will be forced to clamp down the flood of money and raise interest rates.