i have confirmation from virgin megastores that on the 5-disc limited edition deluxe set, the 5th dvd will be
Ghost of the Abyss, the feature film/documentary made by James Camerson back a few years ago.
I got told that for the other 4 discs, the content will be the same as the renound 5 disc definitive collectors edition, which we all know about, by this stage.
description of ghost of the abyss:
You've Seen The Voyage, Now Experience The Only Movie To Take You On A Trip Deep Inside The Titanic. Walt Disney Pictures and James Cameron, the Academy Award - winning director of Titanic (1997), present the groundbreaking cinematic achievement Ghosts Of The Abyss. Joined by his personal friend Bill Paxton (Titanic) and a team of the world's foremost historical and marine experts, Cameron journeys back to the site of his greatest inspiration - the legendary wreck of the Titanic. During the voyage, you will explore inside the entire ship, deck by deck, room by room, encountering mysteries that have remained hidden for almost a century. Revolutionary underwater robots were designed and built solely for the purpose of allowing the explorers to peer deep into the remains of the once-great ship and bring those surreal and haunting images back to the surface world. Loaded with unseen footage, revealing interviews and innovative DVD bonuses, this unprecedented motion picture event is a must-own companion for anyone who loves Titanic.
as for the content on the dvRAB, here it is pretty well explained:
2-DISC SPECIAL EDITION (Europe, Australia and Latin America)