Since BIS added buckshot to the engine, I've been thinking about it a lot lately and I've reached the conclusion that I'd love to see an under-slung M870 shotgun attachment in, say, the HK416 pack, especially on the ACR and 416, with ammo that goes in the same slots that grenade launcher rounds do.
Not meaning to be demanding, just expressing my interest. I do love my shotguns... :p