FlatSix911
Porsche 918 Hybrid
400 kWh in my area is about $42 if they offered it for 20 years at that price it's $840 at the commercial rate this is only $680. This could easily be built into the price of the car.
There are two important factors... First, not everyone will use the full 400 kWh in any given year. Second, as they transition superchargers to be solar and/or off grid, actual electricity costs for Tesla will decrease over time.
On an unrelated note, I wonder if they'll ever sell supercharger gift cards for supercharger credits...
Supercharging will not be free or unlimited for the Model 3.
Remember that the total cost of SC is not just the price/kWh, but the significant investment needed to build each facility.