I didn't really like that NRS retconned her original birthdate to being born in MK2 at first, but that changed when I took a second look at this part of her bio:
"Shang Tsung has created many abominable creatures in his Flesh Pits, but none so twisted as Mileena. A fusion of Edenian flesh and Tarkatan blood, Mileena is both beauty and beast. This dichotomy has made her mind unstable; she is prone to fits of madness and savagery. Though she has the appearance of a mature woman, she is more child than adult--a blank slate conformed to Shao Kahn's will. Devoid of conscience or remorse, Mileena will butcher anyone to appease her beloved father."
That part really interests me because it's true. Mileena may appear to be a mature woman, but in essence, she is still a child since she was created relatively late during the whole Mortal Kombat timeline. She, like Ermac, was created to serve Shao Kahn and she knows no purpose beyond that. And because of these two things, Mileena hasn't been allowed to go through the same psychosocial development and life experiences that the other characters have through. Until now. She was created to supplant Kitana, which already took place when Kitana found out the truth about her "real father" and about Mileena, meaning that she is the true princess of Outworld. That ultimately means as the "true daughter of Shao Kahn", she is the heir to his throne.
What does this all mean? With Shao Kahn dead (presumably for good) and Kitana, Shang Tsung and Sindel also gone, she will soon have to rule Outworld. But there are a few HUGE problems with this. One, as aforementioned, she is still, in essence, only a child, so she isn't mentally ready for such a demanding responsibility. Two, as the ruler of Outworld, I highly doubt her underlings would respect Mileena as the ruler of the Outworld. They would deem her unfit to rule the realm, and being the evil henchmen that they are, it's almost a guarantee that many of them would try to kill her in order to take the realm for themselves. And lastly, Outworld is also in jeopardy now that Shinnok's plans, whatever they may be, are coming to fruition. Remember at the very end of the story, Shinnok said to Quan Chi that both "Earthrealm and Outworld will be ours", so Shinnok and his Forces of Darkness are also planning on taking over Outworld as well as Earthrealm. Mileena, being the ruler of Outworld at that time, would be a direct target of Shinnok. Keep in mind, this would be probably all be happening at the same time. With so much going on, everyone trying to kill her, and no one else to turn to in her time of need, who does she turn to? Earthrealm.
^^^^^ Now THIS is what I envision for Mileena's story in MK10. If this or something similar to it happens, it would allow Mileena's character to grow more and it would make up for her lackluster story role in MK9. She would go from being the typical lady henchman/femme fatale/seductress you see in video games into becoming a character twisted yet strengthened by the events happening around her. The only life she briefly knew as Shao Kahn's daughter has been cut short, and now she is unsure of what to do or where to turn since the people she was the closest to are either dead or trying to end her life as we speak. Are you listening, NRS? THIS is the kind of stuff I want to see from Mileena in MK10, not the horseshit we saw from her in from MK9