An idea I had recently (I was going to submit it officially, and all that rigmarole) might be useful. I'll let you lot be the judge of that.
As far as I can see, we have two problems here. The first is that the female demographic of editors is tiny. The second, and more crucial if we're to work on the first, is that we don't know why this is. We can point to a dozen different things which show why editing in *general* is turning some off, but not (that I've seen) anything that applies specifically - or has more of an impact than it would on men - to women.
One idea I've been playing around with might hit both at the same time. On en-wiki, we've got the contrib team, which is designed to help act as a link between the WMF and community in regards to outreach. We/it have been doing work that involves going to universities, and acting as a gateway for new editors coming onto the site. What we could try is posting a geolocated banner notice that applies to specific IPs of say, Vassar College, a women-only college in the United States. This banner would contain testimonials from current editors (all or mostly female) about how enjoyable it is to edit, the impact editing has made on them, and so on, along with a link to a pre-established gateway to introduce people to editing Wikipedia.
The advantage of this - if it goes well, we get a pool of intelligent, educated female editors to help address the gender gap. If it goes *badly*, we get something almost as useful - a pool of disenchanted potential editors, all from a relatively controlled demographic (reducing the chance of statistical errors) who we can easily contact to work out what exactly it is that hindered them from editing. Either we help address the gap, or we work out *how* to help address it. The only issue I can see is that banner notices don't currently allow for geolocation that's any more specific than the country, but if this idea gets sufficient traction and seems like a good idea to the foundation, I don't see how that couldn't be addressed relatively quickly.*
What do people think? Oliver
*Although I am not a techie.