> It's also horribly energy-inefficient
Yep, here are some comparative carbon costs:
US Military: 59 M Tons 2017. BTC: 22 M tons 2018, 37 M tons 2021, 130 M tons by 2024 predicted in China before shutdown, Banks: 1040 M tons
IMO, the idea of a $1,000,000 BTC would be a huge hit on reducing CO2, as cost of mining approaches BTC price.
> Hork up a bunch of space probes
Here is a variation on that idea: One of the claimed advantages to satellite is lower latency (see https://www.groundcontrol.com/Satellite_Low_Latency.htm) Solana is claiming layer 1 blocktime of 400ms by synchronizing clocks. For Global coverage, I think satellite is a requirement to achieve that throughput as consumer latency is at least double that. This isn't proof of work; Solana calls its method proof of history.
IMO, PoW is the like the Cray Supercomputer of the 80's. My Apple Watch is lot more powerful at -let's see- 1/64,000,000th the cost.