It's a very interesting article. I'm also impressed by such dedication. Hashing the strings from the decompiled APK to easily debug the protocol in Wireshark is inspiring.
On the topic of using a BMW with you phone without being frustrated, some people put a third-party box between the screen and the car infotainment computer to get Android Auto. I heard the experience isn't perfect.
Personnally I use Google Assistant and I think it works relatively well. I can use it to get directions, make the sound of random animals, change radio, play music on Spotify... To trigger it, you can long press the voice command button on the steering wheel.