First, before getting into the gender issue here, which is important, but focuses on a small part of the post: Thanks for the clarification. In particular, I was curious about the role of RFC shepard vs. subteam member, and this is clarified quite a bit now.
Thanks also for this note:
They're difficult to coordinate across time zones -- Rust has developers everywhere!
@nikomatsakis and I are not really that far apart, but between time zones and very different schedules, I'm asleep during most of the time that he's working and online. I've never felt like I would be excluded from the project because of that, but it's a minor inconvenience, and I know that some projects don't consider this as carefully as they should when it comes to coordinating things.
On the topic of women on subteams, I very strongly agree with @mbrubeck's comment. Even aside from the ethical considerations, there's also the fact that having an all-male organization is self-perpetuating. As a bisexual and mixed-race guy, I've actually been reassured that Rust's core team has made an effort to take the code of conduct and moderation seriously, be explicit about a non-discrimination policy, and in general that the community is pretty reasonable (in the places I frequent). So I don't think that the Rust community is hostile to women (and I certainly hope not). But it looks very much like a boys' club if everyone officially associated with the project is male, especially when that's an even more skewed ratio than the tech industry has in general.
I know that if there are unusually few prominent women in the community, the core team and subteams can't just invent people that they trust. But the gender skew is noticable, and an unfortunate attribute of a project that I'm otherwise proud to be a part of.