That all appears to be a bunch of wishful thinking by consumers. The stance of the company appears to be (I'm no insider, by any means, so that's "IMO") that it's considered a part of the car once added. I've seen posts where they've "taken it away" when they owned the car (as in, it was traded in & they later resold it)--that seems legit (though petty), it's no different than removing the floor mats & selling a used car without them. I've also seen posts where folks are saying it got taken away later (i.e., well after the sale). THAT is BS, and I hope if there's any merit to those stories that enough publicity gets made to force the company to do the right thing.
As I said earlier, though: I've not heard of the FSD not transferring with the car to a new owner....