Hmm. . .double bayonet. You wouldn't even need to fire it in the air, you could just wave it around and the Feinsteins of the world would be passing out by the hundreds.
May as well put another Picatinny rail on the bottom of the barrel and go for a triple. And it needs a LASER. And pop-up iron sights. And another flashlight. And a 40mm grenade launcher. Bruce Campbell would approve!
I fully expect to see this abortion in a B zombie movie very soon.
Now if you stripped off the rails, cut down the barrel to 18" and cut down the stock to a stub so it is barely over 24" OAL, it might make a nice shorty to conceal under your duster. Because a double has no receiver, it is going to be at least five inches shorter than a cut-down pump. Also, and over-under would lay flatter against the body than a side-by-side, and would not have the projecting hammers of a coach gun to snag clothing during the draw. I would love to have one with an Andrews Custom Leather Firepower Rig just for sh1ts and grins.
Many lawmen in the old west used such cut-down doubles to great effect. Bill Tilghman was perhaps the strongest proponent of cutting down both the barrels and stock of a double shotgun to make it both concealable and handy enough to use in the tightest of spaces. Even with the tiny stock stub, he was able to instantly shoulder and fire it accurately. His reportedly had barrels less than 10" long.