The Australian Army is evaluating an over the shoulder weapon support system called Reaper.
The system is very simple. In fact it is a modified camera stabilizer. Here is a similar concept by Easyrig. The concept is either a chest rig or backpack system that has a bar that goes up and over the head. The operator hangs a video camera or weapon from the over hanging bar.
Of course I am sure there may be issues with negotiating in and out of vehicles or small spaces and possibly urban environments.
I was concerned about the shooter’s sight picture but it looks like the cordage does not obscure the optic too much.
I think they should have gone the Aliens route and used a Steadicam rig and a MG42 because it would be awesome.