I also don't see the use of utilizing the back of the firing pin as a sight. If the gun is at that height, I will use my sights. It is much easier for me to get a quick sight picture, and it (getting a quick sight alignment) is done almost subconsciously if you practice it a little bit. It would take way more effort to try to retrain my brain to use the back of the firing pin, and I would become less proficient with using my sights in the process.
For an actual close quarters encounter (i.e. no time and/or space to bring the gun to a natural firing position), point-shooting would be a much better thing to train for.