I would imagine the ATF has heard of the 7.62x25 Tok and is aware of its capabilities. If the ammunition being imported now meets the requirement for armor piercing ammunition, it would already be banned.
The length of the cartridge always made it seem a little awkward for a handgun, esp a defensive sized handgun. Even in a service sized pistol, it's a handful. If I am dealing with that sort of grip size, I'll take my Glock 20 and keep it in 10mm. I would imagine you could make the Tok fit in a Desert Eagle, but even the .357 Mag seems anemic surrounded by 5 pounds of metal. Downgrading further makes even less sense to me, esp when you consider the cost of the original pistol and the extensive custom work that would probably have to be done to make it function safely and reliably.
No, what I want to see is a modern 7.62x25 carbine--like a PS90, or even something along the lines of the M1 Carbine or Ruger Deerfield. An AR upper that could take those PPSh 71 round drums would be rad.
Still, your best bet in a modern handgun would probably be a custom barrel and mag conversion for the FN57. The 5.7x28 seems like it is the closest thing in overall length and modern application to what you are looking for and the FN handgun is about the only one on the market chambered for it that I am aware of.