They could still include the mace, but simply do away with the stowage gimmick. After all, other MPs come w/ accessories that don't necessarily stow away. RM Beast Convoy already has forearm guns that pop up without the hands flipping back, albeit with forearm panels flipped up. But of course, that's a 1480JPY (≈AU$15) toy. I would imagine that on an MP budget, they should be able to pull off that gimmick with far more minimalised kibble. Might also be neat to have an interchangeable mouth between neutral and angry. They could possibly even do the same for the beast mode face too.