I have thought for some time now that having an electric heater coil in next to (but behind) the heater core in a car would be an advantage. For the cold mountain mornings, you could turn on the fast-heat electric booster and your fan. The coil would provide cabin heat until the engine warmed up enough
to provide adequate heating.
It would indeed be an advantage when there is a nice thick layer of ice on the windshield.
I say to put it behind the heater core because then it would also help the engine temp rise faster, resulting in less low-mpg-when-engine-cool driving.