im no veteran, but I do know that its speed can only be as fast as it can cool/heat, also maintaining a constant heat on the muscle wire could cause damage to it. Now with a high speed rotor cooling may not be a problem. I also think muscle wires dont have much torque, and in order to move the blades up/down while spinning at a high RPM may require a significant amount of it.
One use i've thought of is for small bipeds, but I dont think they have enough torque, and colling would be an issue.
Woot I love wikipedia, I found this SMA robot: http://www.lararobot.de/
The germans beat me to it, building an SMA robot, pfft. Although it isnt very elegent...