They could use thermal mass to their advantage.... Two easy options:I'm not an HVAC specialist but I think the issue they have is balancing efficiency while using a resistive heater. There no low setting on a heater it just cycles on/off, so to have warm vs hot air running the resistive heater would have to be on 100% of the time mixing with cabin/outside air. Whereas in an ICE they can grab as much/little engine heat anytime. Granted, this is an issue for any EV without a heat pump and Tesla still seems able to hold a setpoint so... hopefully they fix that.
A metal heatsink provides thermal mass. You the resistive heater heats the heatsink, and the HVAC blows air across the fins to transfer the heat. The resistive heater is duty cycled, so it can be switched on/off as necessary. The thermal mass of the heatsink provides smooth, consistent heat to the air which continues to blow, even when the resistive heating element is unpowered.
A heat exchanger and coolant loop is heated by a resistive element. Coolant flows through the loop and air blows through the heat exchanger. The heating element is duty cycled, as necessary.
These are not new concepts. These are used all over the place!
Also, this is yet another reason that a heat pump is great.