First, imagine something that is already a reality … car seats (and other settings) that can automatically adjust themselves to multiple driver preferences. The driver pushes a button, and the seat adjusts itself to a position that is perfect for them. It may also adjust the radio station and presets, environmental settings, etc.
Now imagine that the car has detectors … weight, height, and maybe facial recognition that let it do this automatically, without the button push. As long as the car does not transmit that info to anywhere, I would be okay with that.
For the last part, imagine that if an unknown driver gets behind the wheel, the car enters Hostile Mode. This would not be on by default, and if the person knows a shutoff code set by the car owner, it could be turned off. Hostile Mode would randomly change the seat configuration slightly, change the environmental settings, mirror positions, change the radio station, volume, etc. If the driver does not know the shutoff code, they would not be able to stop this.
I don’t know whether all the bugs could be worked out so it would not backfire on legitimate owners, or whether people would like it, but the idea came to me while riding the train this morning.