The current rap on electric air-source heat pumps are that they are expensive and not-effective in low temperatures (essentially requiring a fossil-fuel backup), points you are making. They seem to work pretty well in places like temperate California. As an engineer, I would like to see more "water source heat pumps", as water sources have more stable temperatures. As you say, the current irony is perhaps more than 60% of electricity comes from fossil fuels. However, when renewables come to bear (perhaps creating 80% of electricity by 2040), I suppose electric air-source heat pumps will make more sense, and yet "what will be the backup source"? This is kinda like powering your house off-grid with photovoltaics/batteries, yet requiring some kind of gas or diesel backup generator. This doesn't seem a huge deal to me, but a problem for green purists. I suppose some parts of the world will ramp up geothermal (a great green heat-source), and the backup fuel might be some sort of biogas (a blend of hydrogen, scrubbed natural methane). My further thoughts are at: https://medium.com/p/5266749a83c6