1. Is this technically possible?
Yes, it is. Likelihood is another question. Right now I'd say the likelihood is not that high, mining is still quite distributed and in addition to that, miners being influenced by government or collectively acting for a country/government is also another topic. In a future where one country dominates all of the resources, controls all of the companies within it/all companies are complicit to the demand of its government, and where other countries have either given up on Bitcoin mining, or simply no longer have resources to compete, that likelihood dramatically increases. Are we headed there? Not an impossibility. Is it happening now? Too hard to say. It'd be quite pessimistic to say that's where we're headed, and that we'll get there with no resistance. 2. What would be the technical implications of China doing this?
It depends, if intent is malicious, they could destroy the whole Bitcoin network by compromising the integrity of the blockchain. The moment the blockchain is modified by a 51% attack, in my opinion, it's valueless. Again, likelihood and actual possibility is something to consider in this topic.3. What would be the geopolitical implications?
That's a bit hard to say. If the rest of the world has dropped it anyway, or there is another alternative, maybe there would be no major implication? Bitcoin becomes valueless, the world moves onto an alternative, and moves on? Maybe a short period of disarray or chaos if Bitcoin is relied upon in some major way and a viable alternative is not yet existent? This would be a controversial opinion, others might argue the end of cryptocurrency as the largest & most supported has fallen. It's an interesting topic.
4. What would this do the broader cryptocurrency sector?
This is even more interesting of a topic. I'd be curious to see if this would compromise the integrity of the entire space or if it would be a temporary transitional period to the next best alternative, as mentioned earlier in the post. I think this also depends on when this happens. Right now, Bitcoin is the most mature chain, if it were to happen today it might have a massive effect that takes a long time to recover from. If it happens in 10, 20 or 30 years, it might be as simple as using the next best thing (or a better thing, if it presents itself between now and then).
5. Have major governments e.g. the US and NATO countries ever (publicly) announced any contingency planning around this problem? Putting a $1.5T asset at risk is something that could rattle the entire world economy. This seems like something they would at least think through?
It's a $1.5T asset however it's not a $1.5T risk or exposure that NATO/US. They have bigger agendas and concerns at this point...I'm not informed on the matter, though I'd be surprised if they're thinking this far ahead.
Good post and great questions
