In my younger days, I was working with plexiglas for one of our jobs. I was shown by coworker that by sanding the edges smooth (belt sander with 80ish grit, and not perfect), the edges could be quickly polished with a torch (we were using oxy-aceteletine) to be as clear as the sheet. The flame was with a welding tip, nowhere near the hottest setting, and quickly moving the flame along the edge. If you lingered or went too slow, then bubbles would be raised and the surface scared. It stands to reason that the same could be done with the kydex, maybe with a propane, map, or butane torch? Worth a try, work on some scrap, could save you a lot of time.