I do not think the CEO was taking about MMO-FPS version of CoD when he mentioned to monetize the CoD series...
He is most likely talking about something similar to Xbox Live Gold. For example, Starcraft 2 players need to pay a monthly fee (or set amount of time, ie, 10 hours connection time) to connect to the battlenet to play others online. So for CoD, you can play single player once you purchased the game, but you will need to pay a fee in order to play online matches.
Unfortunately, this is not a far fetched idea. A few years ago, a game called "Universe at War" tried to use the above business model, but it failed and ended up offering free online matches which are traditionally seen in pc games. I do worry if the game was good and people were willing to go along with the subscription fee. I can see people are more likely to pay monthly subs for the game like CoD or Starcraft 2 if it were forced on gamers.