I'm mostly in favor of the exchange idea too, though I wonder - does it need to be anonymous? I really like the idea of collaboration, and it would be cool to be able to get feedback from the person making the request (or to ask questions). Plus there would be less work on the organizer's end, once the collaborators have been assigned. I really like
Iceea's suggestion too, because I definitely get inspired to write things by looking at art or inspired to draw things from reading fics. If we wanted to do something like that, people could maybe request an art or writing connected to something they've already made (instead of creating a brand-new work to have the collaborator work from) for the first go-round. (Not sure if that makes sense, right now the artist part of me is really wishing I had a minute to like draw up a diagram of what I'm thinking to explain better).
Also, it could maybe get a little hairy if we have different numbers of artists or writers, but I imagine there are a few people like me who are willing to do either, whichever side needs more.
Something for midsummer would be cool too.