I haven't really had time to analyze this cutscene in much depth so i haven't actually come up with any theories as to what it means yet.
The cut scene i am talking about is the one after you complete the final mission. It starts with a brunnette woman reading the numbers into a microphone.
At the very end of the cutscene Mason clearly says "Ascension". I think if someone where to properly analyze the final cutscene they may be able to come up with some good theories as to where the next zombie map will take place, so i urge all of you to go back and watch that final cutscene again.
PS. Sorry if this has already been posted, i tried the search button and couldn't find anything related.
Anyways hope you are all having fun trying to figure out where the next map will be located, and if you do find out anything interesting about this cutscene please do post :)