i did a quick change to see what the player panel docked to the top would look like and it looks very cluttered as-is, so like in your mock-up it would need to "lose" quite a few of the controls to work
In your mockup, there is no back/forward navigation, new tab or refresh button, and no button to switch views.
all of this is probably acceptable to someone who wants a simple player and only uses the main library panel and plays music from there ie. no right sidebar
i do think it would need to have the bottom right player controls though eg. shuffle, equaliser, repeat etc displayed in the player controls panel at the top
i imagine many people would want to have ratings/last.fm love button displayed in the player controls panel