I think there's one big issue for massive electrification and insulation of buildings: renting.

As a renter, I have no incentives to invest thousands in my home's betterment because I will have lost those when I am gone. As an owner, I have no incentives to make my apartment/house better because I don't live in it and I don't pay the energy bills.

Something has to be done about that if we want to combat climate change. I know in France it is now forbidden to rent again or sale when the renter leaves if the home's energy grade is F or G (A is best) but it is probably loosely enforced/easy to circumvent. And it is too damn slow ! This is for regulation but maybe there are other levers ?

As a renter I would basically have to wait for energy prices to skyrocket for it to make economic sense. I hate this situation.

Another big problem is NIMBYism and ideological opposition to air conditioners.

Installing a heat pump can require (city) permits, permission from your landlord (if renting) or HOA/condo association (if you own a flat in a shared building) which can either be or feel impossible to get.

Some cities have either actually or de facto (through requirements/regulations that are impossible or unaffordable to meet) banned air conditioners, resulting in people buying inefficient monoblock units that can't be used for heating.

Edit: Other regulatory hurdles come from rules about refrigerant handling. Refrigerant must only be handled by experts who are certified in proper handling and recovery (and who, of course, are now in high demand and charging princely prices for their work). This made a lot of sense in the times where 1 kg of refrigerant had 10 tons CO2e in global warming potential, ozone depletion potential or other dangers.

Nowadays, a skilled layperson can probably set up an air conditioner with quick-connect couplings by themselves, but they aren't legally allowed to. These cost something like 500 EUR, contain less than 1 kg of R32 with a GWP of 675, so let's say 500 kg CO2e of harm if it leaks. If you passed a law that landlords cannot prohibit installation, and any electrician that passes a quick online training can install them, you could have them all over the place very quickly.

These could then be used for covering some or all of the heating load in winter, but they'd also alleviate suffering in summer, and that's luxury, and we can't have that (especially as it uses energy to provide the "needless" luxury!)

Well, there are heatpumps made to slot into a window frame (ex: https://www.mideacomfort.us/packaged.html ). The ones I'm familiar with are made for double hung windows, which are more common in the US, though. But might be worth a look?