After some speculation, EA has now made the next Battlefield 3 downloadable content pack, Aftermath, official. According to the new webpage EA has created for the DLC, it will come with four new urban maps set in a damaged, post-earthquake Tehran that depict a "struggle for supremacy and survival amongst the devastation". There will also be new game modes and heavily modified vehicles plus new assignments, achievements and dog tags.
Apart from this info there is not much else to share. At this stage it is unknown exactly when the Aftermath DLC will be available for either BF3 Premium or normal players on PC, but hopefully it will be soon.
Source: EA