Summer Glau has been a pretty quiet actress lately; we dont see her in many big films. She mostly works in television. But she is very talented. And she has an established relationship with The Avengers helmer Joss Whedon, courtesy of Firefly and Dollhouse. So she wouldnt have trouble getting her foot in the door. Shes also certainly got the looks to play a female hero. The Wasp certainly comes to mind. She played a very unusual yet, sometimes, physical character in Firefly and she has the small, skinny frame that fits with the shrinking wasp character. Shed suit the wife of Hank Pym nicely. Plus she took a few punches in Firefly...Im just kidding; nobody wants to see any wife beating in the MCU. I dont see her playing any villains; she doesnt quite have the frame to support it. But if she cant be a hero, she could certainly play a good love interest for one of our male avengers. God knows which one though since phase two at least is choc full of heroes who already have established interests.