I’m curious as to whether they’re trying to use the same receiver wall thickness as the original aluminum version. The polymer lowers that I’ve seen for sale are all considerably thicker (longer hammer and trigger pins are not needed, but longer push-pins are).
That was my thought as well, I am very enthusiastic about the 3D process, to the point I may sell one of my gun safe queens to buy an entry level printer, as a machinist and fabrictor who has worked in a fiberglass putrusion and plastic extrusion plant as a die maker I can see ways to change the application.
For the high stress area it may require an insert of aluminum or an engineered plastic like delrin with thicker ribs and longer pins.