Someone already mentioned that your ECU doesn't really need to talk to other systems (besides perhaps via the OBD-II port with a well established, industry stan

Someone already mentioned that your ECU doesn't really need to talk to other systems (besides perhaps via the OBD-II port with a well established, industry standard, backed by regulation protocol). And I'll also add that at no point are you ever going to need to flash the ECU with updated firmware. So while a cute example, it isn't really a practical example. Typically when people complain about "code rusting", it is in the context of a codebase that needs to adapt to the world around it; whether that is communicating with other systems or even just accepting new features within its own little fief.