As of this posting, it is LIVE for Xbox One.
(UPDATE 1:35 PM EDT) It's now available for purchase on PC at least in North America (
(UPDATE 1:54 PM EDT) Available for purchase on PC in UK/Northern Ireland.
There is both a SPOILERS comment (to discuss the DLC) and non-spoilers thread (to discuss issues relating to DLC availability, problems, etc.) on this post. Please put all spoilers about the DLC behind an LJ-SPOILER cut. Thanks!
It is confirmed that the release on 24-March-2015 is X1 and PC only. Bioware cannot discuss yet when it will be live on other platforms (so please don't pester any of the devs about it through social media).
Soon as it is, I'm sure there will be an announcement post on the community and this post will be updated.
(UPDATE 30-MARCH) The DLC is coming to all other platforms in May 2015.
(UPDATE 26-MAY) The DLC is available for all platforms as of this date
The general release Dragon Age: Inquisition "Completed Story" discussion post that was previously pinned can be found here.