I think we've been long overdue for a Zombie themed map. I'm unsure what would be the best way to attack the theme---I could see a map loosely based off the idea of Dawn of the Dead---survivors holed up in a Shopping Mall or some other sort of major building center.
Or I could see a map more based on an overrun neighborhood / city.
The gameplay for either would probably be a little different---but I think reverting neutrals and bombarding would make for some interesting gameplay, and perhaps even an objective of eradication or escape.
Anyways, I just love zombies and want a zombie map to play on!
--Andy