Slight modification to my point as I think I was meaning to say that they could have a separate system in the first sentence. Like maybe there isn't one right now (as you point to by stating that folks have fully disassembled current cars), but they could add one or more as they gain profits from either directly using the data or (more likely) from selling the data.

As for the later point you made about them not bothering for the <0.1% of people. How long is it worth just assuming that they won't do it as they try to find any and all ways to generate profits? They could start moving to the Apple repair tactics of requiring parts to be paired to the vehicle and require "calibration" using their tightly controlled systems in order to have very basic things work correctly. Which removing fuses to those data mining "features" could start shit like a constant system error check light or artificially disable unrelated things.

Honestly feel free to just stick to the top two paragraphs. I went down a rant rabbit hole beyond my initial point. But leaving it here as it still has some amount of value (not sure how much and to whom).

To use Apple again, if you replace a display with a third-party or even a real part but not one they sent you directly (and therefore isn't a valid repair listed for your phone). You all of a sudden get a list of "scary" sounding warning alerts all the time about how the parts can't be verified or calibrated. Which then leads to shit like auto-brightness, truetone colour, and even one or more cameras not working or pictures taken not saving/not being post processed with their software that makes the images look as good as they do. All that because the screen was replaced that they didn't approve of. Sure some things like bio-metrics might make some sense to be disabled due to the non-zero chance that someone could put a hacked part on that could maybe possibly steal your shit for gaining access to your device/account/money. But shit can't dim or do basic shit (even if the replacement is a real part).

Given how drastically so many companies of all kinds are finding it harder and harder to make numbers go up for the shareholders (which is a legal duty to do literally everything possible to do so). Especially as prices for everything are being artificially upped under the pretend guise of "inflation". But it is really more about how they have to charge more so that those shareholders and the top level people can keep making more (but not workers). The level of data mining for passive income is invading all of our shit at levels that really should be freaking more people out. More of these car companies that were bragging about having built-in CarPlay/Android Auto a couple of years ago are now removing them in order to artificially require using rebranded access to them. Locked behind yet another subscription that they can just stop allowing to work every few years. Got to install their apps on your devices. Going to get worse as they find more and more things to "require" having their app. Even if not using your car at the time, it can try to find out what you do and where.

We at the very least need to have all that shit controlled in the interest of users/buyers with very clear legal requirements that at least it be very easy to see a full list of what is, how it is, why it is, and where it is being collected from. And it needs to be legally required that these lists or whatever are written in ways that someone with an 8th grade level of education can read and understand. So no just having an insane amount of super micro tiny legalize TOS stuff like we see with everything currently and hidden away in some cases. Each model of every car with every trim/add-on package should have that list in both print manuals in each car, and have it permanently (and very very easily to locate) on that manufacturer's site.

Every time you take your car to be serviced by tge dealer it's plugged into a diagnostics computer which reads the ECU, with the price of storage it is entirely possible that disabling the cell connection just causes the ECU to write it to local storage for upload at service read. The diagnostics machines are definitely connected to manufacturer servers.

Doing so is trivially easy the telematics is going to be caching before sending, all you need to do is manufacture that cache storage to be large enough (and it's flatfiles we're talking megs not gigs) and tell the software not to delete until it has an an acknowledged receipt of transfer.