Even if that happens you will still be limited to 10 rounds regardless weather it holds 11 or 20 rounds. If there were no mag restrictions I would be all for a double stack 7.62x25, but in a modern design pistol like a XDM or SigSauer, not that there's anything wrong with the Tokarev, I have 2 M213s and they work fine, but the XDM looks really nice and if it can hold 19 9mm rounds it will hold the same amount of 7.62x25.
Correct me if I'm wrong but the 7.62x25 round seems to be the same length as a .45acp, so any firearm that shoots .45acp could be made to shoot 7.62x25, like a 1911, Sig P220, Sig P250 or XD45.
I just checked and a 8 round .45acp 1911 mag will hold 10 9mm rounds but they won't stay in, so I'm thinking a same dimensions mag with different lips could work, seams like all you would need is a .45 frame, 9mm slide and a different barrel.
Just thinking outloud.