So I don't think Tesla is on the hoook because that software feature is a courtesy, not a legal obligation.
Agree. It's not like Tesla disabled the air bags or traction control, etc.,. I can't think of any other mass market car that has a limiter as an option. Regardless, Tesla has no obligation to meddle in family matters. If I ask my brother-in-law to take my Tesla in for service, it would be ridiculous for Tesla to call my wife and I (the registered owners) for permission.