They introduced a new means of killing zombies in every map pack, so chances are we'll see something good IF Treyarch releases MP4.
So far,
MP1: Electric Fences
MP2: Wunderwaffe
MP3: Monkey Bombs
MP4: ????
I'd love to see a new "waffle weapon," perhaps something to do with anti-gravity? Aim at an area of the map (not too large) and gravity is turned off and any zombie that enters this "bubble" will float off the ground. This would be very handy for escapes, since it would literally clear the path of zombies.