> The moment you do this things will stop working: for example phone app

Probably untrue with Tesla. I have mine integrated via BLE to home assistant for solar charging. App works via BLE using same protocol.

Your biggest struggle would be avoiding to update the native app, but I guess nothing is stopping you from developing your own implementation.

Yes the Tesla BLE seems to be one of the better ones and works in the middle of nowhere even without cell reception, so it probably would still work with the SIM pulled on the car side.