An interesting question. Has anybody done any work on this? In particular, how much the stiffness is increased by the centrifugal force of rotation (for an extreme case of this, see helicopter rotors).
E-props are thinner and lighter by virtue on not having the in-plane accelerations that IC props must deal with, and the thin blades certainly seem to be efficient. Can't be getting too much shaking and wobbling, but the theorists among us may point to where the ideal might be. Anyone listening to PW's plane go around can verify how quiet it is.
Our e-props are getting big enough that we might need root hinges soon (joke).
John W