"This is all purest speculation: input from women is needed! Are my speculations wildly off-base?"
Not off-base at all. You're right on target.
Incidentally, while studies show that teenage girls do far better in single-sex schools, the same studies show that teenage boys do better in co-educational environments. If this translated over to the real world, what might you expect to see? Men in male-dominated environments decrying the absence of women but not sure what to do about it, while women form female-dominated groups to work on similar projects in a more congenial environment? Oh look, it's open source software.