Your idea is worth considering. It is like the outrunner brushless DC motors (http://electriccarconversionblog.com/brushless-dc-motor-bldc)
where the outer casing has the magnets and the outer casing is the thing that turns. The stator windings is stationary and inside (but that will still contribute to the unsprung weight).

I guess one could strategically glue permanent magnets to the rim and by having the rim as the “can”, that is where weight savings can be achieved.

Perhaps, also, carbon fiber components could be used in various places to help reduce weight. I’ve seen racing motorcycle rims from the TTXGP championship made from carbon fiber.

I personally would still want to have rotors & calipers for my piece of mind.

Keep the ideas flowing – this is good.

I’m still trying to figure out where the friction brakes are.

Some of the benefits of hub motors are:
* You don’t have to worry about a differential so there’s a weight and space saving there;
* Each wheel can be individually controlled which opens up many new opportunities;
* If you want, you can make a skid steer system (if all wheels have this hub motor) which could be useful in reducing the turning circle of a car;
* You free up a lot of space in what used to be the engine bay (if going for an electric only set up) which can influence future car designs;
* It becomes easier to make many models or variants of cars without increasing overheads significantly. Why? Because the same Electric Motor hardware & set up can be deployed in cars of different widths, lengths and shapes quite easily. With no differential, you don’t have to worry about different width drive shafts that come out of the differential. In terms of length, with no propeller shaft, it makes it easy to make a stretch limo. (I realize front engine front wheel drive or rear engine rear wheel drive cars don’t have a propeller shaft.) You can have the same platform with a different body, a bit like the skate board concept. It helps with common platform designs.
* Allows more room for more batteries;
* Car companies can save on drive shafts and propeller shafts;
* Car companies can save on transmissions; and
* Car companies can provide more interior room as there is not engine to compete for space.

Some of the disadvantages of hub motors are:
* Software gets more complex;
* Unsprung weight increases (as perfectapproach pointed out) which could have an effect on ride and handling;
* How reliable is it in rough terrain (again as perfectapproach pointed out)?
* What happens if a wheel becomes out of balance – will it damage the hub motor?
* What happens if you drive across a shallow river crossing or it is submersed in water like when going down a boat ramp to load or unload a boat?
* What mechanical disengage mechanism is available should it be required in an emergency? and
* Suspension settings will have to be revised significantly.

I know someone who is doing a diy Electric Car Conversion using two Emrax AC Motors (http://www.enstroj.si/Electric-products/emrax-motors.html). They are very small, yet high output. I think it is less than 4″ in length and less than 10″ in diameter. Each motor has a mass of 26.4lbs. He is looking to drive the wheels via a toothed pulley set up from motor shaft to drive shaft on his Citroen to gear it down. That way, he does not have to worry about unsprung weight, no worries about differentials etc.

Personally, I would like to see hub motor technology used in more EVs because it saves space and I don’t have to worry about differentials, drive shafts, CV joints and transmissions. I look forward when Protean makes a kit for diy Electric Car Conversions.

If you have a motor design that is that good, why not use just one that is about the size of one of these, spin it faster, gear it down (to multiply torque), and drive through axles, like other manufacturers do now?