I was wondering... Would it make sense to try to collaboratively develop small settings or modules ? Of course, the main issue is to only work within the SRD monsters and rulesets (I guess that is allowed) to prevent legal issues.
We can use the main Question document for the module text, and the answers for personal comments and feedback.
Even having them as community wiki questions they don't really fit into the Q&A style of Stack Exchange. Maybe if that's all the entire site was dedicated to it might work, but intermixing it with regular Q&A style questions is going to confuse drive-by/new users.
This question is ok, but the answer (IMHO) is a resounding NO (given the SE mandate).
If you wanted to collaboratively work on settings, or even parts of modules at a time, I think you'll have better luck of at the Worldbuilding StackExchange.
Stack is at heart a Question and Answer site. If you had a setting question you wanted a direct answer to, we can definitely help. If you wanted an opinion or a collaborative effort, that doesn't fit within the guidelines of the site.
That being said - You can always make a new Chat room and ask people for help that way!
For a story, maybe...
I think questions* along the lines of "This is some of my story so far; which directions could I bring it in?"
So for example, 1997 Joss Whedon could ask...
[Describes season 1 of Buffy] but then the heroes made some crazy rolls and have killed the Master... I didn't expect this, and promoting his lieutenant to a major villain isn't working since he's like 10. I don't know what direction to take my adventure in!
To which someone would answer...
You could create dramatic conflict by taking that sulky (dreamy?) NPC you described and make him turn evil!
... But the QA format doesn't work for creating modules.
* I was thinking of tossing in a "the question should be Community Wiki" but I should really just get another song to sing. :P
