The world is littered with useless, pie-in-the-sky specifications better suited for garbage pails. And those were written by engineers. Specifications written by management types that don't code are even worse.
After Apache 1, instead of jumping into coding Apache they spent more than a year documenting how they should think it looks. Then with Apache 2 they had an exact idea what to make and it was a true community effort.
codeswarm apache visualisation:
http://www.vimeo.com/1076588Python does the same with the PSEPs.
Remember the python zen:
Now is better than never.
Although never is often better than *right* now.
Free software projects are really excellent when they have to code programs where it's clear what the function is. But when there's no framework or beginning idea in place then it's more a hackfest. That's why much of the best free software projects are opened-up former closed projects (firefox, blender, openoffice, qt, ...)- because now it's clear to everyone which direction the project has to go and the swarm can iterate to perfection.
I have no idea what an exchange site looks like. But having a spec and some screenshot mockups would make it super easy for everyone to contribute a few modules and quickly get such a site done. It's something everyone wants and I'm sure everyone will chip in a small amount of time to maintain their own modules (it's not even a hard thing to code- probably).
We aren't talking about a huge 1000 page documentation bible but maybe 10 pages or so saying screen X does this, blaa blaa.