My main problem with your argument isn't inclusivity (I actually like having female avatars), but the classic line "It wouldn't be that much work!" which always rubs me the wrong way. Nothing in game design "isn't that much work." And anything added as DLC way after the fact has to have some kind of financial payoff. The merc avatars have many many variations. One female merc would likely be as much work as one type of one monster. But the return, looong after the 1.0 release (or even at the 1.0 release) IMO would be minimal.