That is a lot of weight on the handguard.
I am less concerned with the recoil than I am the toque from pumping the shotgun or even just hanging that much weight on it.
Our Night Fighter handguard with the longer barrel nut would be a little stiffer however even then it is a lot for a free float handguard to support.
I think most pictures I have seen of something like this include a mount to the AOW receiver as well as one to the barrel.
The set up you pictured is an interesting thought, but probably not one I would recommend.
Good Luck,
Pete