Activision confirmed months ago that Call of Duty Elite subscribers would get at least 20 DLC 'drops' for Modern Warfare 3, but that was seemingly not enough.
According Joystiq, Infinity Ward is already planning to bring an additional four DLC drops throughout the year. It's not saying exactly when or what the nature of the content will be, but it's coming.
Having a quick look at the CoD Elite 'Season of Content' calendar, you'll noting the Drops count now totals 22, four of which are categorised as "classified".
Best keep some space free on that hard drive.