With the smaller battery on the Model 3, it seems necessary to include a heat pump for cabin heating to reduce the drain on the battery to warm the cabin. There should be a loop that connects to the powertrain/battery to take heat from the motor and move it to the inside of the cabin. There should also be a mode that takes heat from the outside environment if it isn't too cold outside. There would still be the need for a resistive heating element for initial heating, but once the powertrain is warm it could switch to the heat pump. Thoughts?