Interesting certainly, but there are definitely limitations to overcome.
First off, the magnetic field produced by the coils must act over a much greater distance. The strengh of a magnetic field is equal to the inverse of the distance squared. This translates into greatly reduced torque. Additionally, the blades must be ferro-magnetic...that means more weight. More weight and less torque explain the reduced rotational speed. Adjusting the angle of the blades will increase CFM, but will also increase drag thus lowering RPM even more. This might also increase fan noise. Since I've never seen one in action, I can only speculate here, but I'd like to see some reviews on its effectiveness before tossing my traditional fans into the junk-box.