They wouldn't release female skins - if that was the case, females would already be in the game. The reason females are not in the game, is because they didn't want to half ass them (like simply adding skins)
Models - including all the bodytypes and clothing and accessories - animations, sounds, textures, all the extra testing to make sure everything runs smooth - If they had females as DLC, it would be quite labor intensive. I could see them easily charging more than 10$ for it.
Not all DLC needs to make money.
Some DLC is released as support of a game.
A charged DLC might even still lose money, though the price offsets the cost somewhat to make it more acceptable in the books.
The purpose of DLC is to give support to your customers that they want and/or need.
Making a profit is often a goal of DLC... most notably with map packs which practically require purchase, and require little actual programming time, and turn around HUGE profit margins.
Release 2 Map Pack DLC's, and 1 paid but still red (ie; costs them money even with sales) DLC adding more character skins.
Do I expect them to?
Absolutely not.... I think we'll be LUCKY if we see female chars in Brink2 if I'm being honest....
But I'm not saying what I expect, but rather what I'd LIKE to see.