It's not needed. The whole idea of the Lynx is to streamline the platform, not add extra parts to it. FYI, the Lynx (and original AR-180b) already have a rear take down pin... it's built into recoil spring guide rod base plate. It's great because it deletes 4 parts from the rifle and makes existing parts do double duty. It also makes it easier to take down the rifle.
Adding a rear take down pin to the 180 is like car manufacturers adding fake hood scoops to cars.