Here's the official synopsis:
The Cylons began as humanity's robot servants. They rebelled and evolved and now they look like us. Their plan is simple: destroy the race that enslaved them. But when their devastating attack leaves human survivors, the Cylons have to improvise. Battlestar Galactica: The Plan tells the story of two powerful Cylon leaders, working separately, and their determination to finish the task.
The DVDs will include:
BATTLESTAR GALACTICA: THE PLAN - BONUS FEATURES
Battlestar Galactica: The Plan on Blu-rayTM Hi-Def and DVD takes viewers deeper into the acclaimed space drama with exclusive bonus features, including:
EXCLUSIVE TO Blu-rayTM Hi-Def:
* BD-LIVETM: Access the BD-LiveTM Center through your Internet-connected player to download more exclusive content, the latest trailers and more!
o MY SCENES: Bookmark your favorite scenes from the movie.
o BATTLESTAR GALACTICA TRIVIA: All-new trivia game.
BONUS FEATURES (BLU-RAY™ HI-DEF and DVD):
· DELETED SCENES
· FROM ADMIRAL TO DIRECTOR: EDWARD JAMES OLMOS AND THE PLAN – A day-in-the-life with director and actor Edward James Olmos, as he tackles the most ambitious Battlestar Galactica production to date.
· THE CYLONS OF THE PLAN – Features interviews with the actors who play the film's key Cylons, including Dean Stockwell, Tricia Helfer, Grace Park, Michael Trucco, Rick Worthy and Michael Bennett.
· THE CYLON ATTACK – This featurette takes viewers behind the scenes for the planning and execution of one of Battlestar Galactica: The Plan's major action sequences.
· BEHIND THE PLAN - An in-depth look at some stunning visual effects and the role post-production plays in bringing the world of Battlestar Galactica to life.
· FILMMAKER COMMENTARY
I cant wait for this. As much as the finale of BSG left myself and many fans a bit disappointed to put it mildly, it still remains one of the greatest shows of all time Imo. And The Plan looks like it may address some of the questions left unanswered by the final episodes of the series.

Thanks to io9 for all the info.