Could the rotor be shaped like a fan inside the stator of an AC induction motor. And could the stator act as a duct.
Would this lead to a high airflow:materials used.
It could, yes. But the tradeoff would be worse performance. The strength magnetic field is a function of distance from the coil, so increasing the volume by turning your rotor into a fan shape would reduce the efficiency.
Typically, this is dealt with by close mounting a fan, sometimes inside the motor case. The motor stays compact and efficient while the cooling is provided by a fan specially built for the purpose.