... oh sure, of course it works !!!
But, besides being totally exposed to the atmosphere with dirt, dust, mud, water and corrosion implications, there are some other very critical points such as:
1. To produce somehow aceptable power rotor and stator must be very close to each other
2. Axial forces might trigger unacceptable vibrations
3. The magnetic circuit is very poor and so far the output power might be not enough
4. And what about the weight ...