This kind of comment is perplexing to me. I'm always really confused why people try to claim heat pumps are complicated because they're not really (especially compared to many of the systems in ICE cars). Most cars have even already contained a heat pump for many decades (an air conditioner is exactly the same, just moving heat the opposite direction. It literally takes one extra valve to make it bi-directional).

There are videos of hobbyists making heat pumps from compressors salvaged out of fridges or ice makers, and other scrounged parts, maybe an Arduino controlling it! They're amazingly simple when you see what they're made up of.

Sure, it sounds like there were problems with this system used in BMWs, but that's likely just a design issue. Pumping a coolant around a battery and then through a heat exchanger (that is part of the heat pump) is not that difficult compared to the cooling of an extremely complex internal combustion engine!