The KRISS is an interesting concept, but I just don't see it as having much use for regular folks for one reason: the 1934 National Firearms Act.
The gun you reviewed is classified as a short barreled rifle, necessitating the full up NFA hoops in order to own one. For a full 16" barrel, you've just managed to pack a much less powerful cartridge into something the same size as a gun that will shoot actual rifle rounds (more power, more range, etc.).
The lack of recoil in a semiauto (we can't get the full auto ones thanks to the 922o registry closure, which refers us back to the 1934 NFA) doesn't mean much, IMO. I'm not aware of any long gun which has much recoil when shooting a pistol cartridge. Heck, in semi-auto fire, the predominant intermediate cartridges (.223/5.56, 5.45x39, 7.62x39) don't recoil all that much either. Sure, it's a bit more, but remember, we're talking semi-auto fire. If you're drilling bullets carrying a bunch more energy into your target, that tiny fraction of a second from the additional recoil isn't going to mean much- your trigger finger is slower than your recoil recovery.
I suppose there might be times when pistol/longarm ammo compatibility might be desirable, but for the most part, carrying ammo is carrying ammo. I'm just not sure of a situation where we're going to be pulling the mag out of a pistol in order to feed the longarm; if you get to that point, you're hosed anyway.
And all this isn't even considering the price.
I can see how the KRISS in SBR and full auto would be the bee's knees in doing things like house clearing (limited range of the .45ACP wouldn't matter, full auto would be a help, and the lack of recoil would also be desirable), but while it's a neat concept, the real world utility is limited.
As a side note, I was amused when playing Homefront in the final level- the Korean occupiers were packing the KRISS in some instances... I found this funny, since there wasn't an AK variant to be found, but they're using the KRISS in a situation where the greater range and power of a real rifle would have been vital. Ah, well, that's what we get when game developers watch Future Weapons instead of getting out to the range.