I have seen some one wheeled devices around and this is my ideas of using a single wheel as transport. The overall diameter is 600mm and can be ridden with a foot either side of the wheel so you are facing forward or could be ridden sideways with both feet inside the hoop, a bit like a skateboard. All the designs have been done on autodesk 123D Design.
The main wheel is the motor its self, the magnetic hub as a tyre around the outside and the coils on the inner rim which you stand on. The large diameter of the motor means that it will have a relatively high torque for the power put in. It will also allow more room under the feet supports for batteries.
To support the outer rim without a center shaft, there is two rows of rollers around the outside of the inner rim, this means the rim has lots of support and so will hopefully be highly durable.
The turning of a one wheeled vehicle is just done by leaning, like on a skateboard or similar, to stay upright the gyroscopic force of the spinning tyre is used like on a bike. To stop tipping over backwards or forwards while riding electronic gyros can be used to control the motor and add stability.
The batteries that power the whole system would best be lithium batteries. The are expensive but coming down in price. The batteries will be housed in the foot support with a charging port on the side and charger built in.
As you are riding there will be a hand grip control that will control the throttle, display battery level and sensitivity of the gyros that keep it stable.
The bulk of this can be made out of 5 or 3 mm aluminum plate, the rims would be cast aluminum with cast resin around the outside for the coils to be set into. On the outer rim it could either be a cast plastic or a rubber tyre on the aluminum rim with the magnets glued or cast in.
The rollers could be ball races on a shaft with no modifications needed.
Please vote for This in the 123D design Challenge for people under 18.