I think that round would totally be useable to 250 yards out of a 9mm platform modified to 7.62X25. What America needs is a cheap and light PPShK, in semi auto. Keltec could do it easily, with simple barrel and mag mods. I suspect they won’t out of a fear the ammo supply could be cut off with the stroke of a pen.
Unfortunately, no such magazines exist in quantity for a rifle such as you envision. I don't think Kel-Tec wants to get into making a lot of specialty magazines.
It shouldn't be too hard to make a modification of an existing kel-tec design, if you could secure a large quantity of magazines from the east block for the PPsH for example. Have them make a couple of thousand up on special order.
The problem is that these type of guns are already flying off the shelf, and there is no production capacity that is not being used already.