Something which seems to be happening occasionally now is musicians releasing project files or stems (partial mixes) of recordings. Even illegal versions are also appearing, meaning you can change music to sound like you want it to, or take it apart, rather than the producer and engineer.
I've just come across a news article in Sound on Sound talking about a company called Audionamix which is now offering the service of 'un-mixing' audio from stereo or mono recordings. This opens up a whole world of creative possibilities in manipulating existing recordings. There are already a couple of prominent examples: Dame Vera Lynne, being re-orchestrated and the film soundtrack for the Edith Piaf biopic La Vie En Rose. Although the company only offers the service in-house at the moment, I'm sure it'll appear as a plug-in in the near future.
It'll also start to bring up some sticky issues with copyright, as a recording may no longer be 'final'. The ideas of John Oswald's Plunderphonics (even though he had a court injunction to desroy all copies of his music as it infringed copyright, they're still available illegally) and 'mash-ups' can now be taken much further. On the other hand I'm sure it'll also result in a spate of major label re-issues...