It shouldn't be free per use. Sure, most people will likely charge at home, but the minority who decide to abuse the superchargers will ruin the experience for everyone else. Don't underestimate people's willingness to wildly inconvenience themselves for something they perceive as free.
Good points and great examples. One idea I saw on reddit that I really liked:
Supercharging is always "free" for all cars. However, if you sit in a charger spot after your charge is already done, you will be charged a "late disconnect" fee. Maybe $5 for the first 10 minutes, maybe $40 for the next 20 minutes, etc. This way, you can only blame yourself if you get fined.
Also, this could be extreme, but for maybe for time's sake, at the peak of peak times, they disable 90% to 100% charging because it takes so long. Since there will be so many more superchargers, nobody's trip will be made impossible.
Do we know if the SC sends back info or if the car sends back info about it's charging. According to @wk057 currently it doesn't appear to care what the VIN is, just that you have the bit for SC enabled at the car.
It definitely does! But, not sure if it's unique. But, they know how many cars are charging at a station. That info will be integrated into the nav with an update so it can plan around busy chargers.