This. "How do we get more women in OSS?" is the same as saying "How do we get more male nurses"? If men want to become nurses, then they will become nurses, if women want to become open source software developers they will become OSS developers.
That's true only if there are no institutional or cultural barriers. From reading the experience of women who are interested in OSS or men who are interested in becoming nurses, that does not seem to be the case.
The only exception really is to look at institutional (not cultural) barriers IMO. "Are we doing something that keeps people from being willing to have a seat at the table?"
Cultural barriers are beyond our immediate control where they extend beyond an immediate institution. If nursing is seen as unmanly, then there's not a lot one can do about that. And very often well-meaning attempts to "fix" cultural problems ends up re-inforcing them. Culture is a very resilient, homeostatic thing, and indeed, the idea that "we know what's better for women than they do" is pretty obviously sexist, but it is the same thing that comes up when saying "how do we get more women involved in X."
In general the only culture you can change is that of your own institutions, including your business and your family. That's it.
Edit: Downvotes are a bit amusing. Guess someone finds the idea challenging?
You could be right, of course, but a lot of the weaker responses to feminism have the same basic "no point in trying, ladies" conclusion that you do, and turn out to be suspiciously convenient for the speaker. So anybody with much history in this is not going to have time for resistance-is-futile comments whose supporting evidence is, "Gosh, that looks hard to me."
That goes double for startup people. It's par for the course that half of everybody tells you your idea is wrong, unworkable, impossible, foolish, or dangerous, and that you shouldn't even try. You quickly learn not to listen to those people except to see (so rarely, alas) if they have some novel point.
Are you an anthropologist, to be able to say how resilient culture is to change? Can you produce some studies to back up this claim?
How do you explain the anti-slaving and civil rights movements? They didn't take 1000's of years, yet the idea black people were inferior was pretty deeply ingrained in the white culture's psyche.
Saying "we can't change the bad things in our culture" is self-defeating and destructive.
Just because it's not your forte does not mean it cannot be done. There are people who are quite skilled at "hacking" culture. Also, culture is not that homeostatic. One of the things about gradual change is that it goes unnoticed so that people take it for granted that "this is how it has always been" when, in fact, that isn't true. Culture evolves over time. The trick is to help it evolve more in step with the times instead of having a huge lag. It's often the degree of lag-time that creates huge friction and pain.