Certainly can appreciate the concern of a drop out failure or a tube failure. If it fails, ce la vie. The frame and fork alone are 7 pounds. the thing is a tank. If the stays are less than .9mm at the ends, it would surprise me. My guess is they are more likely 1mm. I did give thought to brazing on brake mounts, however in the future I can remove the brake adapter and have a completely stock frame. Not that it matters, but I find something of value in that.

The picture of the Roloff hub and drop out failure looks like the brazed joint failed. Am I seeing that correctly?

The torque arm on the drum is necessary in order for it to work, without it the pads simply spin with the hub when applied. Same principle as a brake arm on a kickback hub.