Again, that's already done in large part with the new supercharging fees for cars ordered after January 15. I've not surveyed every state, but it seems that in many states, the charge is on a per minute basis. Once you get above 80%, that minute delivers less and less in charging, so you increasingly paying more for less. It doesn't take long before those electrons get pretty expensive.
For those where supercharging is charged by the kWh, it seems that Tesla is charging at least the "going rate." Take OP's home state of California as an example. While OP appears to be paying 48¢/kWh,
THIS SITE states that the average rate in California is 15.34¢/kWh (according to the U.S. Dept. of Energy) and the average rate in OP's home city of Whittier is 15.98¢/kWh. Tesla's supercharging fee in California is a flat 20¢/kWh, a substantial margin over either average. While I understand that tier pricing may very well raise costs well above the average for either Tesla or the average homeowner, it does not seem that Tesla is providing power at such a discount to draw folks in.
We still do not know what sort of allowance, if any, Tesla will include with the Model 3. Heck, Tesla may not even know at this point (I wonder what sort of hand wringing happens in those meetings). I cannot imagine that it would be more than the S/X allowance of 400 kWh/yr, and I wouldn't be surprised if it were less.
Those that never charge below the annual allowance likely will not be much of a factor because they just don't do that much supercharging. Those with FUSC will become less and less of a factor as their number contracts and the supercharging network expands. In the end, there just aren't going to be that many "Larry Locals" or FUSC owners around when compared to the supercharging population. Everyone else is paying up.
As a footnote, I still disagree with OP continuing to refer to this charging as "free" or "for free" as if it were some sort of mooching and not included in the price of the car.
