So what I was thinking is that I dont know much about technology and how to create a rolling canvas, so I think this could work. I put together a basic concept using some of my contest entries to test this. I started with a canvas size of 1280w x 960h 300 rez. once the first picture is added that artist could post it to the thread, then the next artist doubles the width to (2560w) uses whatever space he needs to integrate his idea and posts his integration to the thread and so on and so forth...
Here is what it would look like after a couple of artist submit their integration into the roll...
http://imgur.com/a/4k5FA