>For example, how many are in China or the U.S.’s reach? Because that means literally two people, Xi and POTUS, could round them up and effect a change. (Not saying they would. But a damning vulnerability for a libertarian ideal.)
Actually, that's exactly what Xi (or the CCP, if you like) did[0] a month ago.
And I’m extremely happy about it. Xi had the power to concentrate all Bitcoin miners in China and use it for a 50% attack (even though there would have been a huge uproar about it), it was the weakest point of Bitcoin. The US president doesn’t have that authority / power, states have powers as well, and there are other institutions that provide a counterbalance.
Actually, that's exactly what Xi (or the CCP, if you like) did[0] a month ago.
[0] https://www.reuters.com/world/china/china-central-bank-vows-...