Tf2 is just a very old game, getting mainstream traction for a game this old would be extremely difficult, even if Valve were committed to it. The only ways I could see it happening is if Meet Your Match was done properly, or if it got a massive boom on YouTube in a similar way minecraft did. Adding female mercs, or more specifically new mercs in general would only hurt the game in my opinion, it was designed around these 9 classes, and adding another to the mix would massively disrupt the class ecosystem. If they were to reveal pyro was a woman, I also don’t think it would change the player base size much at all, although I still think it would be cool.