Not related much to your realtime co-editing vision, but I have really appreciated the upload/download to OpenClipArt feature in terms of allowing others to help with my projects even without necessarily knowing it, and me doing the same in turn for yet others. I guess my wishlist item would be for this existing feature to become just a module in a framework for other repositories to upload to and/or download from, in particular Wikimedia Commons.

-Arlo