Currently the Magpul FMG9 is a prototype, but the possibilities are amazing. It is built around the use of either a Glock 17 Semi Auto or a Glock 18 Auto, both are 9mm. I suspect they could include the Glock 22 in 40 or Glock 31 in .357 to the list since they follow the same dimensions as the 9mm versions.
Using the semi auto options they could market this to civilian sales on the Class 3 market. They could potentially make adjustments where the folding action does not expose a stock, but just the grip. Doing that would allow them to mass market the design as a concealed carry option. Magpul could make a pocket pistol that would have no imprint using something like a Ruger LCP or even one of the 9mm pocket pistols on the market.
Based on what Magpul is saying on their website, a folding concealed carry pistol without a stock may be an option: “Magpul FMG9 (Prototype) featured on Discovery Channel’s Ultimate Weapons. Production version is called FPG (Folding Pocket Gun)”