The USTPO has just published a patent application by the owner of MD Arms. The patent describes a double stack magazine for a shotgun. MD Arms is best known for their MD-20 Saiga Shotgun Drum, so it is no big leap in logic to assume MD plan on producing a double stack magazine for the Saiga shotgun.
Feeding rimmed cartridges reliability is no easy feat. There is good reason why so many rimfire magazines fail to feed reliably and why most shotguns have tube magazines. Is the rims of the rounds are not correctly aligned jams or misfeeds will occur. The MD concept allows the rounds to move forward or backwards inside the magazine, but as the lead round is being pushed towards the follower, channels in the side of the magazine guide the round's rim so that the lead round is always position correctly for feeding.
I am sure many Saiga fans are going to be overjoyed to know that a double stack magazine for the Saiga is in the works!