There better NOT be another one because if they do the explanation would be worse than like X6 "I repaired myself while hiding in a cave" or X7 "guys I have returned from my 100 year sleep after 2 months due to popular demand." That is unless Z5's main character was Neige. I swear Kraft's moves are all made for a human being, and I can see Neige just put on like a mecha suit (or better yet come up with a human interface with whatever Ciel was working on) and grab Kraft's arsenal and start doing the same moves (okay she probably can't lift the knife gun or carry the 500000 missiles Kraft uses for his EX move, but everything else is fair game).
But even then, there would be nothing more to kill. As far as I can tell Neige is the remaining leader of humanity with Neo Arcadia all but gone now and she finally agreed to accept the Reploids, so what's there left to do?