As much as I like the notion behind this idea, it's difficult for me to get behind it.
Any good female gamer knows not to open her mouth in voice chat. I remain an absolute mute when I'm on my xbox in PvP games, if I know what's good for me (I game for enjoyment, if I want to be harassed, I'd go outside)
But League has let me chat freely and communicate with my teammates without the stigma of being a female in a PvP game.
and lets face it, especially in PvP, the chatter can get a little rough.
and it's a little sad that female players feel the need to hide themselves when I think about it, but at the same time, I've been gaming all my life and this has been the norm.
EDIT: I know I can still use the chat function over the voice option, but as somebody mentioned before, people will tend to ignore the text chat in favor of mics.