Maybe I'm being myopic as far as the definition of firmware. I've never heard of a firmware update for a car, but if it's not happening already, it'll probably be part of the regularly scheduled maintenance in the future.
The term "firmware" originally referred to code that ran from nonvolatile memory, such as EPROMs. Originally these devices weren't electrically reprogrammable; you had to pull them off of the board, erase them with UV light, and burn your new code and data onto the chip with specialized equipment. Firmware was also commonly shipped on mask-programmed ROM chips that were cheaper than EPROMs but that couldn't be reprogrammed at all.
Essentially nothing like that is used anymore. Almost every programmable part is reprogrammable in-system unless someone takes extraordinary measures to prevent it from happening. That means that there is no longer any real distinction between "firmware" and "software," and there is no such thing as "read-only software," as you put it earlier. There is only "software" and "locked software."
This thread is all about who should own the keys to the lock.