I wouldn't discount it so fast. One country attempting this doesn't mean much but one success story? If they can make it work other countries will follow. Then game theory takes over
Yeah, but most other countries already have their own fiat currency. In the unlikely event this actually succedes,i still don't see why it would threaten US as global reserve currency or otherwise make a difference.
It threatens the US as a global reserve currency because everyone knows the US can inflate away the value of the dollar at will.
Decentralized trust is the exact reason why some digital currency, like bitcoin, may eventually replace the dollar as a reserve currency. That is the game theory aspect, in relation to the US dollar
Ongoing geopolitical events on the other hand (e.g. rise of china, changing energy geopolitics) probably do a lot more to reduce usa's influence