Completely disagree with the OP's idea of putting this in a rear-view mirror. One benefit of a rear-view mirror is that things that are on the right side of the mirror are to the right of you, and vice versa. This mirror would break that, unless I'm misunderstanding it.
I'm interested in what applications this may have, if any really. I can see it working as a vanity mirror quite well, as then you can truly see yourself as other do. Aside from that?
The rear-view mirror mentioned by the article in passing is not a reversing mirror -- it's just supposed to be another example of this guy's expertise at fabricating mirrors, in this case to improve the field of view and to remove blind spots.
I'm interested in what applications this may have, if any really. I can see it working as a vanity mirror quite well, as then you can truly see yourself as other do. Aside from that?