Okay, I don't know how workable this is, but perhaps a rethink is needed. This idea would only take off if a number of fansubbers took part in the creation of the site, and therefore it would make it pretty difficult to start up - yet, it could be a better method.
I propose, rather than making it solely a place where ads from groups are put up, make it something more personal, and let every potential fansubber who joins have a profile that would look something like this:
Name: FalseDawn
Position: Editor/Timer/QC
Current groups: Umai, Ureshii, Solar (etc.)
etc.
Then, we could have a status - such as "Looking for new project" - "Not looking but open to requests" - and "Do not bother this subber." And perhaps, a list of upcoming projects they are looking forward to potentially work on in the upcoming seasons. Mine would look like:
Projects I'd Like To Sub: Baccano! Clannad (Toei Movie), Nanatsuiro Drops (etc.)
You could also have group profiles, detailing projects groups would like to work on and what positions they're looking for (it would be up to the group to edit the page - possibly a passworded wiki).
However, I envisage downfalls in this idea. For example, unsolicited PMs becoming more rife (perhaps there could be some sort of customisable filter could handle this?) and the sheer number of groups/individuals you would need to join to make such an idea workable -
especially the number of translators, as they will be (as they always are) the most sought after. To be honest, this is a pipe dream and I think you'd have to sacrifice a whole lot of time working on a site that could do all that.
And yet, I live in hope that something as awesome as that could be created. It'd certainly make the fansubbing world feel a lot more cosy
*sits back and waits to be flamed*