Why? dual rotors are expensive but more impotantly I suspect the cause of most of the failed gennys here is largely heat which would not be as bad a problem on this design. This design scales very easily and creating a more durable genny is also a consideration.

You are right in that the design will not allow for any adjustment after it is built. The only way to change it would be to tear it apart and rewind the coils. I do not see that it will be any more difficult to build then an axial or more expensive for equal power output. I would have to build a small one to test so that I could get an idea of what a large one will cost.....