On Rage today we had almost every level 80 player online in a Raid and after 3 hours could only get the Sept. World Boss down to 80 percent health. Now unless you intend players to spend 15 hours trying to kill this thing, Funcom, your plan didn't work.
So, I suggest that the World Boss has maybe three versions that all have the same loot tables, but are adjusted to the number of players on the server when it spawns.