The one essential problem with any DVS, no matter how advanced actually is, is the fact that you still need a reliable source of music and a way to upload music to your playlists.  This act alone can take many hours to do if you have hundreds of songs to go through.  It gets worse when you begin analyzing and tagging songs, only to realize you have missed a few files that you wanted.  Out comes the trusty USB drive and its back to the drag and drop method.  Many of us do not like filling out laptop HD with thousands of songs, nor do we want to give up an extra USB port to attach an external. Streaming music would definitely solve many of these problems – but it also creates problems in the process.  For one, music that is meant to be private has problems being used in a DJ setting.  There are of course the obvious copyright laws – since the musicians aren’t getting paid to have a DJ use their music.  Secondly comes the moral problem once again.  It isn’t so much what you think and how you use your music – but it is really what others think of your habit and how you are judged.   http://www.djtechtools.com/2014/02/05/dj-with-spotify-pacemaker-ipad-app-review/