China is in no position to replace the US$, probably ever, as they seem to have hit their demographic-economic limit.
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I agree with your statement about China.
Your statement also got my mind thinking about this question.
When do we in the United States hit our demographic-economic limit?
Demographic? Long ago.
Economic? Coming soon. US cultural rot is spreading and consuming the piled up cultural and human capital. The US is hanging on only because of the immense reserves of value accumulated by more virtuous generations. It takes time to burn through that.