The YouTube Cast Receiver plugin is available for testing. It allows you to cast videos to Volumio from the YouTube mobile app or website for audio playback.
You can get the plugin here:
Follow the instructions there to install it (and also go through the rest of the Readme so you have an idea of what to expect). For Volumio 2.x you would still need to update your MPD unless you are fine with playback cut-offs and don’t mind seeking not working.
You can raise issues here as you find them, and feedback is of course welcome.