These are hardly new. There was the Pancor Jackhammer and the HK CAWS, both of which never got past the prototype stage, the AA-12 was in development since the '70s, and only one full auto scattergun got past the prototype stage, and that was the Daewoo USAS 12.
In theory, they sound good, but in reality, their use is limited to specialized roles due to their limited range, high weight and bulk of the ammo.