I have Android Auto in my car and virtually all of the data usage is Music. I think it would be really nice if they would try to pre-load music that I'm likely yo enjoy when the phone is connected to my home wifi network, instead of always streaming over mobile. The other day I drove for 2.5 hours and it used 300MB of data. I wasn't even listening to music the whole way.
It takes some planning ahead, but I use a podcast app that automatically downloads episodes when I'm on Wi-Fi and I explicitly download a few playlists on Spotify.
