[beiller]

Ah I see what you meant by "work can't be useful", apologies. But I think you did jump to some conclusions for example, increase of difficulty does not require more miners. It is a side effect of miners joining. So the profitability of existing mining infra in server racks will go down due to the difficulty increase. It would most likely incentivize them to also somehow recycle their "waste heat" for profit. My comment elsewhere is maybe devoping space heaters that do computation (maybe hashing is not that computation but I think it can work), we could use them to migrate off existing heating tech used in my country (natural gas furnaces) and net lower greenhouse gas emissions because not all electricity is generated from greenhouse gas, only some, and it also has a path forward to no green house gas emissions from electricity generation.

[goodpoint]

The value of any PoW coin is based on the sacrifice being made. Something is valuable because you are throwing away something else that was valuable. There's no way around it.

Regarding heating things with electricity, a heat pump is way more efficient than resistance/mining heating because is moving existing heat from one place to another.