Or, maybe, it is possible to have optional library list in tab, like "web", "playlists", "computer" in left navigation panel? It would be even more convenient. Because all those tabs are optional, it will not add clutter for those who don't need it. For those who need, it will be only one click for changing library.
Reason for few libraries is for having different libraries for classic and contemporary music, two temporary libraries for music organizing purposes, one library locally in computer for music located in the laptop.