Perhaps NewScientist’s Feedback column (6 January 2018) has foreseen the capstone of the energy problem of Bitcoin:
If this trend continues, it won’t be long before someone tries to build a Dyson sphere, enveloping the entire sun, to power the trade in cryptocurrencies. Which perhaps explains why we haven’t heard from any Kardashev type 2 civilisations yet – they are all busy mining bitcoin.
The dedication of the entire civilization to the discovery – or validation – of a currency. I’m sort of boggling at this right now.