I play e-guitar at home and I'm used to play my favorite songs by playing with backingtracks. There has been a website that has provided a really huge database with tracks where one or more instruments where removed from the original audio track. Unfortunately this website seems to be offline since a few days.
Since you have the rights to provide us with nearly every song that exists it would be a very nice upgrade to Spotify if it can provide a possibility to create my own backingtracks from my favorite songs on Spotity by deselecting the instrument audio trace that I want to complement by playing it by myself.
I found e.g. a backingtrack for Seek and Destroy of Metallica but it is not of good quality and it is without both the lead and the rhythm guitar. I would love to have a chance to select the instrument by myself that I want to play on a high quality song.
I'm pretty sure that in the Spotify community many musicians would love such a backingtrack tool, since there is no other solution available that brings both the music files and the tool.
I hope this idea will find open ears and minds. It would make me really happy.