I was looking through my item.dat and I saw at the very end was "GENDER 0;0"
Were genders a planned feature that got axed or would it have had different default heads or something?

probably a thing for knowing which gender the user is for the sounds and the default head texture.
don't trust me these help squad will reply anyway with the same answer because im wrong, isn't that right help squad?
i'm just a man with no formal education

It does change sounds and head texture like oxide said.
it's possible to change on item.dat and on the forums(edit details > gender).

Here's the reason:

interesting, thanks for the info!