If the question is about deciding what kind of heating to use, more likely than not the choice will be for new gear. For a new house the choice would be between one of the modern furnaces or electric heating. For someone with an old furnace, the choice would be between no change, a new furnace, and electric heater. I haven't checked the payoff and environmental cost of a new furnace versus no change, but it seems relatively likely that also in this scenario the competition to electric heating would be a new furnace.

Would electric heating mostly use electricity during times when solar or wind is abundant? If not, then, until storage is widespread and is efficient, coal might still end up being used to satisfy those customers' requirements and the mix would be worse. Electric heaters that store heat in a large mass exist, but that approach wouldn't work for mining rigs.

I don't dispute that electric heating can be better than gas/oil, depending on location. But I still don't believe it's the majority of cases. And again, this ignores that in many cases the best solution would be a heat pump. If the argument is about making cryptocurrency mining ecological, it would be disingenuous to ignore that alternative.