Yes...I must say..this is the first I have heard about this panel and the outreach seeking women panelists. Including my involvement in numerous open culture mailing lists...(but, perhaps I missed an email seeking participants in my crazy life!).
I know a few women who might or might not be in London, but who might have interested in this (from academia and the open culture/knowledge world internationally)... all it would take is a few chances to send a call to action to mailing lists.
Not really sure what to say regarding how to deal with having an all male panel. I'm sure it won't be the only one. This is Wikimania after all...and based on our gender ratio....
:)
Sarah