So, as another point of reference, a T/C Contender frame and the rest of that family line, can be built to be a pistol, as can the AR-7 Explorer. But not Restricted.
If the mounting attachment for the stock is such that a hangun grip cannot be attached, that takes the 'handgun' argument out of the picture. Or, it should.
The potential for flying crap, from the cylinder/barrel gap, and that it's boot ugly, are pretty much the main reasons I wouldn't care for it. But, there's something out there for everyone, isn't there?
Cheers
Trev