What I'd like to see, and what I don't think has been done before, is a survey of editors as they are editing. By that I mean, when someone saves an edit, a box asks them "What was the purpose of your edit? What made you decide to make this edit? If it was to correct an error, how were you alerted to the error? Do you have specific expertise in the topic of this article? Are you male, female or decline to respond?" etc. etc. It could be done alone, or in conjunction with a broader opt-in survey, but I think it would capture some really interesting and useful results.