I don't think this is the most natural interpretation of the Joker. I would opt for rules where the Joker keeps mimicking the previously moved piece after null move (just as it would after opponent Joker move).
I agree with HG. It makes sense that a joker imitating a king to be a man so KJK is exactly like KMK.
I agree with HG. It makes sense that a joker imitating a king to be a man so KJK is exactly like KMK.