The more we electrify our cars, the less feasible this is.

Decoding and sending messages to mechanical systems over the CANBUS is one thing (still difficult, but possible), but taking control over system software is another. In the us, consumers are supposed to have the right to repair their personal vehicles, but a lot of that law was established back when you could do work on a vehicle without having access to digitally protected copyright. We might have a right to repair, but that's starting to clash against their copyrights over their IP and software controls.

And that's not even getting into their eagerness to utilize subscription models - would a court side with a consumer if they decided they wanted to circumvent DRM controls over subscription-controlled car features (a car that they own outright)? It's unclear to me that right to repair or consumer protections have been written in a way to accommodate those conflicts.... Especially when cars are subject to far higher safety regulations than computers - a manufacturer could argue that they need to prevent consumers from tampering with their software systems for their own safety.

If you still own a 'dumb' car without one of these systems, it's really not a bad idea to hold onto them for as long as possible. You can always upgrade them if you want to - some people have even replaced ICE transmissions with electric ones. But once you own one of these cars with software-controlled systems, it's far harder to strip them out. Especially once they start requiring cellular connection to operate or function (or require connections to privately-owned satellite constellations.....)

Or just disable the cell modem.