I can see this idea as a 2 part exercise - firstly collaboration in the writing of a piece, and then the mixing.
So lets say for example someone sets up a Sonar template under a specific music genre. The template has say a maximum of 12 tracks set up in it. The tracks could be anything specific to the genre choosen but lets say we have drums, bass, 3 guitars, piano, 2 synth, vox, 2 bv's and a loop track. Twelve people nominate for each project to write and record one part on the template ie they nominate guitar 1 or bass or main vox etc etc. The project is saved as a bundle and maybe Dropboxed around to each project participant who then adds their part and uploads it again for the next person. It would be interesting to see how the piece develops as each part is written.
Once all parts have been written and recorded, it then goes to say 3 mix guru's who nominate for each project to take the tune and mold it into the finished product. We would then have 3 variations of collaboration for each project - it could get extremely interesting!!
This way, each "Community Project" would involve not only the talent pool of mixers out there but also the artists.
Obviously there would need to be a facilitator for each project to keep things on track and there would need to be guidelines in place like who starts each project? Does it start with a vocal, a melody part or does it start with a groove or just a guitar part? Also do the mixing dudes just use Sonar plugs etc etc. And to keep things ticking along the facilitator would need to ensure parts are recorded quickly and moved on to the next person.
Could be fun!! Hope this adds to the collective of ideas!!!