Blender itself is a collaborative community project, and for the open movie Sintel there was a call to sprint model assets. In the end I think a bunch of planks or crates did get used as filler objects in the market place scenes.
BSE at its heart is a QA site, and the focus of this community is to provide people with working answers. I think something like the Blender Cloud is more attractive as a potential platform to explore Massively Multiperson Online Artistic Productions. (Like MMORPG, MOOC).
It isn't clear to me that discussions about these kinds of things and how they might manifest has a home on BSE-Meta either. You could test the waters in the Renderfarm chatroom, and if that gets serious a dedicated chat could be made.
My closing remark is that I too have thought on occasion that if every strong contributor to BSE had sufficient free time, and interest, and could agree on a collective goal/project we could do some wild stuff -- but that's a lot of ifs.