It depends a bit on how houses are built and how the culture of keeping them maintained is. Here it's feasible for most home owners to renovate. My house is from the 80ies, so some work is required, but not much, to get things compatible with a heat pump. Adding false walls in older houses is common though. The beauty is that these things pay for themselves.

Also, opening a window if it's too hot (in winter) was never a rule here, we must save a penny wherever we can ;)