Appetize.io has released support for audio output on Android. To enable it, add query parameter &audio=true in your app URL. 

Here's a demo version to try out! https://appetize.io/demo?audio=true&device=pixel4&launchUrl=https:%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DU03lLvhBzOw

There's no current timeline for audio output support on iOS, but it is currently in development. 

There is no planned support for audio input, i.e. microphone, at this time.