> The Nordics tend to have their buildings designed for heat pumps from the start

My grandma's house from the 1950's wasn't "designed for heat pumps", neither my other grandma's house from 1940. Neither was my mother in laws from the same period.

You don't need to design anything, you just need a hole in the wall to run the cables.

What does make the houses suited for heat pumps is the fact that Nordic houses are designed to keep the weather out. So when you heat/cool the inside, the house doesn't leak it all outside.