Looks to me like 1942 or 1943 is comming.
the Premium Calendar it says very clearly on March 2013 "get a sneek peek footage from an upcoming expansion"
https://2img.net/h/i253.photobucket.com/albums/hh64/Nimmer/1943_zps937b20d2.jpg [i253.photobucket.com]
Add to this the easter egg tank from 1942 on a new aftermath map
https://www.youtube.com/watch?v=ObythfEkyyU [youtube.com]
and I believe there will be a 1943 expansion before BF4