You might be right. But we have no idea what the potential warranty liability is at this point. We're not even 100% sure it's possible, so no way to know the implications. Personally I would not pay $5k. But $1-2k I think I would. It would be hard to convince my wife at $2k, but it would be a non-starter at $5k. "You want to pay money so you can drive like a maniac and risk your life???"
Tesla does have a history of this with the battery capacity, and I'm liking the situation to that one.
Now if Tesla upgraded a big number of older, say all 2017 manufactured S75D, for FREE, then the marketing value around that is enormous. Potentially worth way more than the $2k/$5k/$7.5k/whatever that people might otherwise pay. Imagine the headlines "Tesla increases 0-60 performance by 1s for all 2017 cars on the road, OTA, for FREE!" This would be absolutely groundbreaking in the automotive world. It's one thing to add new features. It's a whole other to make massive performance improvements.
Anyway... all just speculation for the fun of it.