To follow on from my earlier reply, but with regard to your last sentence specifically: "If they can layer on system security without compromising occupant safety, they will, but not at the expense of crash survivability."
That's a non-sequitur in this case. The correct viewpoint should have been "if they can connect to outside networks without compromising occupant safety, they will, but not at the expense of anyone's safety."
Once you have chosen to make such connections possible, layering on security is not optional. If they say they can't do that without impairing crash survivability then don't create the security risk in the first place.