I am not saying that chainfire from the aft side is not possible. Of course, it could happened. However, from what I found, majority of chainfires started from the front.
Talking about flame propagation from the back, that is the reason I like idea of using those elastic sleeves over primers. And if I am not mistaken, elastic sleeve reduces cup's disintegration. Unfortunately, I cannot find video.
However, I found something else; option of using small pistol (boxer) primers with plastic sleeves, instead of percussion cups
Cheap Black Powder Shoots - Quick Tips - YouTube . That elastic sleeve should hold a primer in the place, and also prevent flame from igniting primers (and powder) in other chambers. Very neat idea. Searching now stores in my area to find suitable elastic tube. If my Ruger Old Army could take small pistol primers, a big problem will be solved. Those percussion cups are sometime hard to find. On top of that, in my area, they are 10 times (yes,
TEN TIMES) or even more, expensive than small pistol primers.