They’re already using them in Finland. And there’s a company building them for residential applications

If you take something not unlike a water heater and fill it with sand that you then heat to about 1,000 degrees farenheit. Then when you need heat you just pump some air through it and use that feed of hot air to provide heat where you need it. And unlike heat pumps, this can be added to the sort of baseboard heat you find in a lot of older homes.

And since the heaters are just simple resistive coils with 100% efficiency, it’s a simple and cheap way to store electricity that you’re going to use for heating anyway. Remember that every time you change energy from one kind to another you’re going to lose some of it in the process.