Well, that did not work.
My geometry had a flaw. I could not tame the horizontal distortion away from the midline of the visor. Rotating the geometry sideways was not invariant unless the projector is half the distance to the mirror. A modified surface worked to some degree but the field of view was limited by increasing distortion towards the outer corners. While the ability to see the world through the partial mirror is nice, it is not a big enough FOV to keep the topic alive.
Sometimes my investigations hit a snag, and this was one. Best to not keep digging the hole deeper. I have unpublished the latest post, though I will leave the earlier ones in place as their contents were correct, as far as they went.
There will be a few weeks until the next topic, enough time to be sure it works before getting started.