Could still contain it though. Bluetooth would only be needed for the non critical sound/calls/navigation stuff which should be it's own separate subsystem, on

Could still contain it though. Bluetooth would only be needed for the non critical sound/calls/navigation stuff which should be it's own separate subsystem, on a read only OS with boot chain security so even if you did find an exploit in the bluetooth stack, it would only give you access to very unimportant things, and only until the car reboots. Of course I don't expect it's implemented anywhere near securely, but in theory it's very possible. Game console companies have this stuff pretty solved.