It would be nice to see Glock make a carbine the same way Hi Point and Beretta do. I don't have much use for one, but I'm all for options.
In the mean time, you might want to check out MechTech
. A bit pricey for me, but a good way to turn your sidearm into a main-arm in a hurry. I'd consider getting a compact unit with telescoping stock, but can buy a levergun to use, which lets me keep my pistol on my hip as a back up, for around the same price.
Still, not a terrible idea.