I can't even conceive that China, Russia, etc. would one day demand payment for anything exclusively in bitcoins unless they're well aware that the countries they're selling to have enough bitcoins and are willing to deal in that.
Also, there's nothing stopping the US government from simply using BTC itself, or whatever cryptocurrency it sees fit, as it might any foreign currency.
I've never seen any sign that the Fed or the USG actually see cryptocurrencies as a threat.
Again: cryptocurrencies have built in anti-inflation mechanism: you can have just these many bitcoins. You can't inflate out your debt using printing press. Very good feature for a creditor nation, like China. Very bad for debtor nation like the US. Ie The USD monetary base at least doubled since 2008. To deal with the debt. Impossible to do with bitcoins. Or gold for that matter.
Also, there's nothing stopping the US government from simply using BTC itself, or whatever cryptocurrency it sees fit, as it might any foreign currency.
I've never seen any sign that the Fed or the USG actually see cryptocurrencies as a threat.