In what should come as no surprise, Daelo from Blizzard, announced that Icecrown Citadel is going to be gated in much the same way TotC
was. What this means is that the whole raid will not open up when it is released. Instead a new wing will open up every few weeks, and heroic mode will not be available until you defeat the whole raid.
World of Warcraft - English (NA) Forums -> Icecrown Citadel Raid Access Progression