Update (March 24, 8:37 a.m. Eastern): The Jaws of Hakkon DLC is now available on both Xbox One and PC.  (Correction: The content doesn't seem to be live yet on PC, we apologize for the false alarm).

Update (March 23, 8:25 p.m. Eastern) Due to a technical glitch the Jaws of Hakkon DLC is available now for purchase on Xbox One. EA will not be moving to pull it down, so have at it. PC players still need to wait until tomorrow, though. 
The DLC includes new enemies, new legendary armor and weapons, and the brand new region of Hakkon. Happy hunting!
Update (March 23, 4:44 p.m. Eastern): EA and BioWare have another surprise. The Jaws of Hakkon DLC will be out tomorrow, March 24, on Xbox One and PC. Surprise!
Update (March 23, 2:27 p.m. Eastern): Following the achievement list appearing online, EA and BioWare have confirmed the first DLC for Dragon Age: Inquisition. The trailer will be available tomorrow, but one piece of information stands out.
The DLC is launching first on Xbox One and PC. There's no mention of a PlayStation 4 release, but given the use of the word "first," we assume that it will be along at some point on that platform. We'll share the trailer as soon as it's available tomorrow.