I assume we all remember the infamous Model 1887 shotguns from MW2, correct?
Well, in the new SP trailer that was posted earlier tonight, a very quick shot is shown a man on a motorcycle pursuit, and the man whose eyes you are seeing this through is holding a single Model (The scene is also very reminiscent of the motorcycle chase in Terminator 2, just BTW (anyone?)). Here are two shots I managed to grab:
As you can see, the first picture just shows the one 1887 almost exactly identical to the Models in MW2. The second depicts the same badass flip-cocking that we saw with the Models (Akimbo'd) in MW2
Now, as to whether or not they are the fourth and classified/unrevealed shotgun in MP I do not know; the same goes for whether or not you may dual-wield them. I personally think that, at least in MP, they should keep it to one model only *Prays to god*, akimbo shotguns are just a little ridiculous. However, I thought this was pretty cool, and the trailer was definitely badass. Feel free to discuss!
EDIT: The Models will Not be in multiplayer, they are SP exclusive -
http://www.callofduty.com/board/viewtopic.php?f=70&t=284998&p=3433758&sid=tc48qisht3vg8b48dqb7bu8qe7#p3433758