I don't know the answer to my original question however I did buy a Chevy Volt extended range EV with Android Auto and both are great. The car also has a built in nav system which I haven't used because Google Maps on Android Auto is so much better. Android Auto gives you Google Maps, streaming services like Pandora, iHeartRadio, Tunein Radio, your Google contact list so you can make phone calls and call up directions using Google's speech recognition. It doesn't respond to OK Google prompts, you have to touch the microphone icon on the screen but otherwise the speech recognition works as expected. Android Auto is only on a few cars at the moment, by next year it will be on most cars. I limited my car choice to cars with Android Auto so that limited me, my short list at the end was the Audi A4 and the 2017 Chevy Volt, I got the Volt.
BTW I have Android N on my 6P so I can attest that Android Auto works on N.