They're great tools that are available for a tiny fraction of devices, usually only after jumping through hoops, thus failing to invalidate the claim
>> Not even most Android devices have facilitations for that.
(Emphasis mine)
Edit: my intention was there is no official way of doing it, and conveniently forgot to say so in my original comment. That was unfair on my side, sorry.
A random car from a 2nd hand car lot with a mystery custom firmware? Oh hellllllll no.
This only add value if you assume there are no bad actors. I'd bet $100 if this becomes common, 2nd hand car lots will sell access to install creepy tracking firmware on all cars that pass through their hands.
Just like any random car can have a $100 GPS tracker or spy microphone hidden which you won't locate without dismantling the entire car.
If someone wants to spy or be nefarious with a car I can think of many easier & cheaper ways than making custom firmware for the radio.
exfiltrates private information like contacts, SMS,etc..
sends premium rate SMS's/spam contacts
trackers
bitcoin miners
virus
adverts
etc...