Strictly speaking this was revealed last week, but I have been away from my instruments, and therefore unable to continuously monitor The News. DICE have said there is a fifth BFBC2V map, but it's not going to be available right away. Why not? Well, it needs to be unlocked. They explain: "You and all your friends playing on PS3, PC, or Xbox 360 need to perform 69 million team actions across Battlefield: Bad Company 2 and Battlefield: Bad Company 2 Vietnam. So what’s a team action? Well, it’s any and all of these: resupply, revive, heal, spot, and repair. We start counting on December 21st, so make sure you contribute from the start!"
Hmm. There's a trailer for this shackled map, below. Exciting!