Adding new weapon types that require new graphics to the game at this point is extremely costly, so that won't be happening I'm afraid.
That said, I too would like to see shotguns and I'm sorry now that I haven't included them from the start. So if I ever decide to add another weapon type, like through an expansion, DLC or some such, it will almost certainly be shotguns.
Dual wielding would entail even more cost in graphics and a bunch of coding in many aspects of the game, so that won't be happening.