I really don't see why this wouldn't be doable. There's already a thread for avatar requests and one for signature requests, so one for art commissions in general shouldn't be too farfetched a suggestion.
Plus there's the fact I always feel weird about taking time out of people's days to ask for things like this, so it'd benefit me in particular because the only people who would really be looking are artists who are looking for something to do anyway.
