Thing with carbon is most people assume that people go with it for weight advantages, and this is often not the case. Carbon is used particularly in forks because with carbon, unlike many metals, you can change the characteristic of the tube. This is done by altering the type of weave (the thickness of the strands) and the lay-up pattern (the angles of intersection if using multi-dirctional or the angle of laying the uni-directional fibres). By doing this you can make a carbon tube strong, yet stiff in one direction and more compliant in another, depending on the circumstance. The aluminium equivalent will be light and stiff, but with no compliance at all. I personally wouldn't use a hub motor on a carbon fork, but if weight is your reasoning for considering it, you would be far better off looking elsewhere on your bike to save weight. You could fit some Easton forks, but again with light weight comes a sacrifice, and personally I would not want to sacrifice on the area that holds my motor!
Another thing to bare in mind about carbon is that, like everything else, there is cheap carbon and there is expensive carbon. Cheap frames are made in one piece, with no ability to inspect the internals after the curing process. This leads to high failure rates and unreliability. Alarmingly many manufacturers still use this method! Once built it is incredibly difficult to tell the difference.
The expensive stuff is made in usually 2 or 3 seperate moulds, where the tubesets are inspected before finally assembly, another mould and more curing. This means your resin percentage (amount of glue left in the frame) is particularly lower, hence lighter and stronger. Having seen the inside of the tubes before assembly also means any imperfect ones are binned before final assembly, not "discovered" by the end user when it snaps!
I can feel myself rambling now so will stop typing and eat my lunch