There's that word again. Depends upon how you define free.
Many M3 owners won't use SCs and will happily not pay for it. Think of them as Leaf clones.
Further, many M3 owners will in fact have "free" SC usage presuming the higher packages include it.
One can certainly envision, as with AP today, a 30-day trial or some sort of annual plan.
But what will not fly is poo-poo. People who say "Oh, I'll use SCs once in a blue moon." Actually, you'll use them perhaps 15-20 times during a single round trip from LA to Portland with time built in for sightseeing. Do that once a year for 5 years and exactly how much money do you save after 100 poo-poos versus just paying up front?
Lastly, your point is well-taken regarding the garaged grabbing a quick top-off at an SC before heading home. This will lessen as activity increases. Again - you'll see usage at SCs primarily from distance travelers and from the non-garaged. And that's exactly what Tesla expects.
The question in my mind is how much of a fire Elon and the Feds can light under private enterprise and municipalities to build out infrastructure in the next 4 years. Because by then it won't be just Tesla in the game. But Tesla will have the best network and the garaged STILL won't use SCs locally to any significant degree
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