Cool idea. Good use of a disc compatible hub. Once you get past the issue with the cones, I think you will have a uniquely personal fixie.

If I were to undertake this conversion, I would probably carry it to the extreme and cold set the frame to 100 mm. Of course you have to consider the chain line which could be a deterrent, but I would cold set as narrow as possible, for both strength and appearance.

Of course, this is from someone who doesn't understand the cycling community's fascination with fixies, and knows for a fact that he would never own one.

Good luck on your conversion!