When a tech is new and cool but still not evolved to practical.
My friend, there is nothing "new" about this technology. It has been around for ages. As a child I lived in a home with a heat pump, and that was in the late 80s. I'm gettin' pretty old here, and heat pumps are even older than me. Heat pumps are just air conditioners with one extra part: a reversing valve that allows the direction of flow to be switched so the hot side of the system can be inside in the winter and outside in the summer.
Heat pumps don't require further evolution to become practical, they're already practical. Beyond practical! It's a heating technology capable of efficiency greater than 100%. It's called a "heat pump" because the system doesn't create heat, it moves heat. From outside to inside in winter, and inside to outside in summer. Since a heat pump is not creating heat, instead moving energy that already exists, it's possible to get more energy out (in the form of heat) than the energy you put in (in the form of electricity). Generative heating technologies (natural gas or oil furnace, resistive electric heat) cannot match that as they will always be below 100% efficiency.
I live in Canada, I have a heat pump, and it is great. If you think heat pumps are bad, or not suited to northern climates, or not yet practical... I'm sorry, but you're misinformed.