Being 12 gauge alone wont protect it from anti-gun scrutiny.
The anti-gun representatives in Congress will use the NFA law and the GCA law to look for ways to restrict anything they think is a good candidate for political attack. Congressmen know they can get Brownie points with their party if they step up to the plate and swing at political issues. If they make a home run their party often holds them as heros. Antigun people held Clinton as a hero for pushing and signing the Assult Weapon Ban, puting a stop to all thoses Chinese semiauto imports, and stopping the Chinese ammo imports.
The 12 gauge street sweeper type guns were banned because of the NFA law allowing the Government to restrict guns that happen to have a bore diameter over .50 caliber. It was determined to be unsporting. Unsporting has been used to often to try to eliminate politically incorrect guns like semiauto rifles AR-15s, AK's, and others. Nothing is safe from political attack.
A new extended 12 gauge shell could just as well be attacked like the .50 BMG has been. The .500 S&W magnum became an immediate target not very long after it came out. The antis tried to make the argument that it can penetrate body armor. Someone could easily say this new extended 12 gauge round is capable of blowing up buses, air planes, and killing innocent children 20 miles away. When your dealing with political liers like Feinstein, Boxer, Kennedy, Clinton, and others anything is possible. Anyone can make some kind of law preventing the regular public from having guns. But, as of right now this new 12 gauge creation is safe. Its legal until otherwise.
On another note, I do think this new cartridge has great potential for shot loads too. I wonder how many 00 buck balls can be loaded and shot at maybe 1200 fps.