There is a theory that the USD as global currency is at risk of being replaced due to BRICS. Often the RMB is posited as the successor to the dollar, but I don't think it is possible to use a currency that is not openly traded, nor for which we have insight into how its value is set (not derived by the market, but set by the country itself) as a vehicle for secure, stable exchange of value.

Of course, the current administration is doing a good job of running the USD down, but even with that I don't see how any other currency can replace it for the foreseeable future...

Full disclosure, I am not an economist