Even if the US starts buying BTC for its reserves, I don't believe that the EU would follow that example, let alone China.
If the US starts buying BTC as a reserve plan, that sends the signal to every other country that BTC is better reserve currency than USD. And since the entire world keeps reserve in USD, it'd encourage everyone to dump USD for BTC.
If the US starts buying BTC, we should expect other countries to follow. But, I doubt the Fed will resign its position that easily. They're not going to allow this, so in my opinion, until we see the actual bitcoin reserve plan in action, we should remain humble.