Making a completely collaborative documentary film is an interesting idea.
The one person who has done the most research & work in this area is a nice fellow named Kent Bye. He's making a doc called The Echo Chamber Project.
Check out his most recent post -- imagining what you might do combining Final Cut XML with something like Drupal:
Collaborative Media with Drupal and Final Cut Pro XML | Echo Chamber Project:
I just wrote about the Choice and Freedom that XML provides consumers of products from software giants, and I'll talk a little bit more about some of the implications of being able to export Final Cut Pro projects into an XML format.