Just a thought. There are Aguila mini shells on the market. Their distribution is limited by the unreliable feeding in standard action shotguns (2-3/4”-3”). Development of a short 1-3/4” action may accomplish both reliable feeding of mini shells and higher capacity at the same time using existing mag feeding systems.
It’s a section of the market that has underutilized potential. Shorter, faster strokes, smaller external magazines for box fed shotguns...
That is a whole new topic, but I am going to answer it here.
"Just a thought"
If you are able to think, that means you are human.
"There are Aguila mini shells on the market"
I did some research about this type of shells and yes they have some advantages over regular, conventional shells... for double barrel and pump action shotguns.
"Development of a short 1-3/4” action may accomplish both reliable feeding of mini shells and higher capacity at the same time using existing mag feeding systems."
First, developing a new action from the ground up for just one type of ammo would be useless and too expensive to make (economically speaking), even for a brand like Mossberg, Remington, Browning/Winchester ect... "If it ain't broke, don't fix it", since the problem does not come from the gun, but from the cartridge. Shorter means less powder, less powder means less gas pressure (also less recoil), and less gas pressure means no enough gas for the piston to run the action, that is why it fails to extract (because extraction is the first problem with those shells, even if you chambered only one mini shell, feeding issues come after that...). This was the example for a gas operated shotgun (since I do not trust the Remington Versamax), but I am sure mini shells could work in inertia operated or short recoil shotguns (not sure for long recoil actions tho), if you want to keep it semi-auto. This type of shells is meant to be used in double barrels, single shot and SOME pump action shotguns (with modifications), so manual actions. Also, do not forget that 12ga shotguns are meant to be versatile firearms, so you can shoot all types of loads without making "any" modifications to the action or mechanism. If you decide to make a shotgun that can only shoot mini shells and nothing else, you totally miss the point and nobody is going to buy it because of the price of the gun, price of the shells (around 15-20$ for a box of 20) and lack of parts since it is a new design.
"smaller external magazines for box fed shotguns..."
At this point, if it is the magazine that bothers you, buy an AR pistol like a CMMG Banshee in .45ACP for good firepower, more capacity, glock magazine compatible and less complexity, because a 5 mini shells magazine is ridiculous.
Or keep the high capacity and put it in a regular sized box magazine by converting it into a horseshoe-like magazine (sorry for the bad drawing)