The problem with most alternative refrigerant technologies (magnetocaloric, electrocaloric, thermoelectric) is the same: the temperature deltas tend to be rather small, at best 25 C. That is roughly the thermal performance of the recently published "ionocaloric" cooling system; 20 C is very good for a magnetic system. For air conditioning, a delta of 25 C will just do (assuming outdoor temperature below 50 C!), but heat pumps may need to cross temperature gaps of 40 C or more.

I remember reading about this in Popular Science in high school. Residential refrigerators powered by this technology by 2006! Twenty years after that magazine article I haven't seen any substantial progress towards a commercial product.

I for one, hope that someone figures out a way to make this cost effective.

I think thermoacoustic coolers are another promising solution.