If you want the actual stems of the song, that would actually be the music in it's pre-mixed form. It wouldn't even be mixed at that point, let alone mastered.
Or you could crowd-source them but then it might go against the creators intentions...
(Very) Basically the camera's recording goes through a process to make it into a standardized ACES colorspace. It will then being processed by editing, VFX, grading, etc... and then there's output transforms from ACES for each output device, like a cinema projector, a home TV or a mobile phone.
And yes, AFAIR, that does need grading for each targeted output device, because of how we see and perceive color depending on the environment we're in...
It would be awesome (EDIT: to have something like that) for music as well
I also wish more bands would release instrumental mixes of their albums, like Imogen Heap, Celldweller & Blue Stahli have done. Sometimes I want to listen to an album while I work but the vocals are distracting. I've been happy to pay a few dollars extra to get the instrumental versions when available, it's an easy way for indie bands to make some extra money from fans.
Some exist: http://news.traxsource.com/articles/1754/stems-announced-at-... only four tracks dedicated to designated instruments. I've also heard of iklax http://www.iklax.com/
But how granular would that get? Would I be able to listen to one of 50+ layered distorted guitar tracks on "Siamese Dream"? Would anyone want to do that?
There are some fascinating isolated tracks out there, but I wonder if knowing that stems will get released will push things in the studio even deeper into the territory that every recorded note must be perfect. Making a record already produces a lot of self conscious anxiety that affects your decision making, so knowing that people will also be listening to and analyzing your individual tracks is even worse!