That said, no one isreplacing NatGas with Electric Resistive Heating, that would be crazy, NatGas is still cheaper in most cases for people north of say KY but there are alot of HeatPumps going in
I am unclear why you think replacing a NatGas heater with a HeatPump "would not increase the total electricity usage at all" that is just false, and I am not even sure why you would claim other wise, NatGas is not an Electric Fuel Source so when you change from a non-electric fuel source to an electric fuel source you will use more electricity. Now changing from Resistive Electric to heatPump would actually drop your electrical usage in some cases (above 0degrees anyway)
Around here it is not uncommon to have a HeatPump with a Gas "emergency" heater for when it gets too cold for the heatpump, as Electric Resistive is TERRIBLE and expensive. The problem is when that combo is sold normally it is wiht 80% furnances or they just leave the old furnace in place and just upgrade the AC/Heatpumpt