Well, the problem with the heat pumps in my house, is that near or below freezing temperatures, the outdoor unit has the tendency to freeze over, then either it has to run its resistive heater, or intermittently cut out and blow some cold air inside. It's rather uncomfortable.

I'm not sure you can get away with a design that has to sporadically turn itself off, and melt itself down in an EV.

Heat pumps on cars can go well below freezing without any issues.