It already works this way
! Tesla knows which car is using which supercharger at any moment. That's how they were able to contact people that were abusing the supercharger system.
This is a common misperception. The poorly-worded letter, evidently written by an intern, approved by legal, and then once blessed, as is often the case, considered sacrosanct prior to distribution, was sent to numerous owners who had never supercharged or who had only supercharged for distance travel exclusive of those areas served by Tesla's commitment to DENSITY as well as to DISTANCE (so stated since late 2014).
As for the other well-meaning, common, and wholly wrong assertion concerning pay-per-use schemes antithetical to Tesla's mission, see this:
What wasn't said.
Happily, it seems reasonable that the base Model 3 will offer both supercharging and AP convenience features as post-sale enable-able for a one-time fee upgrades. This is analogous to the first Mustang being released without a radio, as Iacocca at the time (yes, he was at Ford then) wanted an as-low-as-possible price point for what was intended to be an affordable family sedan.
What's going to be particularly interesting (and hopefully we find out at the 2nd reveal prior to the M3 Design Studio going live) is the final initial range options for the M3. The greater the range, the less pressure upon SCs, local and distance, and around and around and around it goes.
Seriously why does someone give me a dislike for a perfectly valid post.
Hopefully the above answers your question. For additional clarity, we could insert "also" into the relevant sentence. That letter went out to a whole bunch of people. The majority offenders at the time seemed to be livery owners (taxis/cars for hire) who at least in LA/Orange Counties have been known to use SCs 3-4x/day. Garaged owners are rarely so penny-wise and pound-foolish as to waste their time at an SC; I did meet such a (new) owner at SJC one time - she thought it would be a good idea to use a busy SC while her rate plan changed over (which would take a month). We gently reset her thinking. Unfortunately, like many urban myths, it only takes one real example to cause those not at the few affected locations to think that there's an actual problem in need of solutions such as pay-per-use. Not the case at all - with again, the possible exception of livery. The livery pressure has been seen at Schiphol (airport) as well as a few counties in the US. The other 98% of SCs seem to be largely underutilized, and Tesla has responded by adding more SCs to those areas to which they have committed (DENSITY).
