I'd like to call to your attention an article I've just posted on the FSFE's website.
https://www.fsfe.org/en/fellows/modulus/user_driven_software_development
That's an interesting approach. RMS mentions the possibility of founding an organisation for a certain feature or project in a few speeches. What you are suggesting is rather like a marketplace for such "organisations" which makes a lot of sense to me.
Btw, we are working on something very similar for a few months now: Flouzo (http://flouzo.net/). It's not exactly the same, as the scope is broader than Free Software, but it certainly is within our goals, and it came from the Free Software world, in a large part *for* the Free Software world, with a reasoning very similar to what David described in his article.
For example, our first campaign is currently financing a GPL violation lawsuit in France (see http://freebox.flouzo.net/), and one of the campaigns currently being prepared will attempt to finance the development of a FS alternative to Google Reader. We also made the Ryzom.org campaign back in last December. Be nice while reviewing Flouzo though - we are still in early development / alpha stage, most of the features aren't here yet or are still clumsy. But it works! ;p
So, if you decide to push the FUDS project further, we'd definitely be interested in helping/participating/financing/whatever. :-)