Google recommends to limit amount of browsing in Android Auto to avoid detraction from driving. If too much of browsing functionality is detected, I am afraid, Google might remove app from Android Auto capabilities and prevent future application submissions.

You still can play or shuffle a folder by using your voice, and if folder name is matching, let's say artist name.

For example you might have an artist "Pink Floyd", but also a folder, named "Pink Floyd".

If you say: "Shuffle pink floyd", Muzecast will shuffle Pink Floyd folder, but if you say: "Shuffle by Pink Floyd", Muzecast will shuffle artist named "Pink floyd".