I am the Kat that Walks By Itself

Illo-a-thon sounds like a great idea if you can find enough artists. Could you just start a comm for it, get as many people as possible, and then make it clear that you'll match people up as closely as possible, but can't guarantee that every story will get illustrated? Then writers can give detailed headers for their work, and artists can specify what they're willing to illustrate as narrowly or broadly as they like.