Spotted it in the video when watching it, instantly googled an image. Looks pretty sweet to me! Not sure what it could do though, obviously has a scope on it.
a shotgun with a scope that makes it a LITTLE bit more accurate at mid range but otherwise has no further effect?
Maybe when looking through the scope... you can see cloaked spies (maybe have to activate it and it dies out) for a decrease in damage? Maybe... just maybe. Either that, or increased accuracy most likely.
Cited from TF2 Wiki: In the trailer for the Mac update, the Engineer is seen holding a brand-new shotgun with detailed engravings, a device on the side, and antennae. It is also notable that this shotgun has a stock, as well as a seemingly longer barrel than the standard shotgun. The stealth inclusion of a "Laser pointed" Sentry kill icon, and the fact the shotgun features an antenna, has lead many to believe that this shotgun could theoretically paint targets for the sentry gun, allowing it to shoot over much greater distances, and allowing the engineer to choose target priorities.
Actually a pretty good target, the sentry won't be distracted by a scout who recently drank bonk when a heavy comes in to blow up the sentry, or it will shoot the medic first if a heavy and a medic come in together, unless they're ubercharged.