IMO, most people who buy carbines are interested in either shooting targets/plinking without the recoil and expense of a large rifle. You don't need a near-specialty pistol cartridge to get low recoil out of a long-gun, and you could easily shoot .223 for about the same price as .357 sig so there is not a price advantage.
For a real world use on living and reinforced targets, it might work pretty good for the intended purpose (although like Mannlicher stated, 10mm would probably be even better). But I suspect that there is not a justifiable market there anymore. Most police and militaries have gone away from the pistol caliber carbines/sub-guns to compact full power carbines. So the pistol caliber stuff out there now is basically just for range toys, and who wants a range toy that shoots expensive, not as common ammo?