Thanks Spectre for remembering an overlooked gun. Too bad it isn't selective fire.
The Kel Tec does have some positive aspects going for it. Its compactness makes it a prime candidate for concealment. Shared magazines with the pistol is another feature favoring its adoption.
Besides selective fire, what would be nice is a shoulder holster akin to HK's PDW holster - one that unfolds the stock and locks it into position while the weapon is being deployed.
Since I favor the high shoulder position for pistol calibre carbines, I don't really like the Kel Tec's butt. A HK91/93 collaspable stock butt is more natural for mounting of the firearm in this manner. For those of you unfamiliar with the high shoulder position, it brings the gun sight closer to eye level and requires less tilting of the operator's head, thereby preserving as much peripheral vision as possible.
If Kel Tec makes a model to take a 10mm Glock magazine, I'd bring one home.