Another gun that I can't see being in the twilight war was the ever so popular HK CAW. Germany has never been big on shotguns period. So they are gonna jump from having no shotgun standard to this super shotgun that can fire special flechette rounds effectively out to like 150-200 meters.
Shotgun magazines are bulky as hell, because the ammo it holds is also. This limits the amount of ammo you can haul around. So the thought of a soldier with maybe 6-7 10 round magazines rapidly blasting away with it seems not very likely outside law enforcement or elite units. This was another gun that was tested, but do to the ending of the cold war the (CAW) program just went away. If it was that great the U.S. military, who is a big user on shotguns would have gone ahead and grabbed this baby up. It was just another show boat piece just like the OICW. All hype with no intention of really taking off.
If I played the game, the only way I would let a PC or NPC have such weapons would be if they where a person directly involved with it like a civilian lab tech/engineer or a military dude that gets to play with/test futureless weapons.