What a waste of resources. Millions of devices will now add to the landfill, despite nothing is wrong with them in terms of technical funtionality. Just because Spotify wants them do be discontinued.
It should be law that when a manufacturer decides on discontinuing an otherwise fully functional product in such way, they should be forced to publish the source code of the software used for the respective device as well as any other resources for free so that users of these devices at least have a chance to repurpose it.
This also stands for any "smart" / internet-of-things-devices where the main functionality is reliing on the operation of a server. When the servers discontinue their services your device is basically a brick with no other functionality.
Short answer is GPL3 doesn't just require source disclosure for the software delivered but also software or firmware that it requires to function.
So say a network video player under GPL2 would require release of the player source code to whoever you give a copy of the player software to you wouldn't have to give the source code to the video server that it needs to work with because you didn't give them a copy of the server.
GLP3 would require you to also give the server code. So if the car thing was under GLP3 they would have to give the server code and people could run their own server for it.
That's a simple explanation. In reality it's more complicated but that's the gist.