I have zero problem with contributing tracks from one of my songs to see what people do with it. I collaborate a lot with a friend in England named Mark Longworth and it's always fun.
We could make it a "flash mix" - I could post something using hightail.com, where you can download for a week or a certain number of downloads, whichever happens first. Make it quick, and keep moving along - then it's someone else's turn. I think only SONAR plug-ins is a good idea, but I think it might be best to strip out as much stuff as possible other than the tracks themselves.
What would be even cooler is if people could replace/remove/add parts, not just remix. If anyone wants to take this further, people could go to my YouTube site and we could get a consensus on what people wanted to remix ("Hey, that song sucks, but I could make it
really good!"). There are 15 pieces of original music in addition to the covers.
Let's see what ideas other people have.