I don't think it's fair to expect users to update something safety critical like the software frequently. If software needs patching, this is comparable to a manufacturer recall. Automatic updates is a rather dangerous idea in the event that the security is compromised by hackers.
I think there needs to be some clear policy on what users are expected to do to keep the software up to date. Something like requiring it is updated manually by engineers during its one or two year service seems reasonable.
This would also make sure that cars are changed over gradually (in the event that somehow some malicious software did get on them).
Biting the hand that feeds IT
