The right one is the "similar media" tab. It collects the similar songs and bands to the currently listened song. It's actually already in the Noise app as a feature. I don't know which database is the data from, but it actually works. If you click on the song what you want to listen/download/buy, it redirects you to the last.fm (in your default browser), so I guess it's using the last.fm's database.
Nice... for my taste this should be all the things the a music player should do. XD (Show the album/list of songs, let me have a simple/quick searchbar, that is all. d: )
Harvey's mockup was showing the album details view like when you select an album in the grid view (if I'm not mistaken). So it'd be instead of the decorated window we currently use.
I don't understand the right tab.
It's actually already in the Noise app as a feature.
Ultimately the side panel has potential, but I'm not sure this is the best way to use it. I reallly wish I could be more helpful with my feedback. :/