It always interested me, because I felt Icecrown would have given a huge chance for us to fight some older characters, maybe even more lore characters. The Lich King is an obvious fight, but what about the Spirit of Ner'zhul? Now with him being destroyed by Arthas inside the Lich King's mental landscape, Ner'zhul could be played out as a seperate spiritual entity similar to Mathias Lehner, only hostile. We have the obvious returning character like Saurfang Jr. and Bolvar Fordragon. If Blizzard really wanted to go nuts and tie in a few other the secondary storylines of WOTLK, they could have it so one of the dragon bosses is a ressurected Malygos.
Actually, Chris Metzen hinted in an interview that Arthas may steal the powers of Malygos following his death, gaining the energy of the Aspect of Magic and growing in might, and my own personal theory is that the Lich King will even absorb the powers of Yogg-Saron. What better way for the "Death God" to grow in power then consuming the true "Old God of Death"?
When I heard about the 31+ bosses, I though we would have a chance for a lot of those lore heavy fights, but now, looks like we going to have to trim down to the more respectable 14-15 bosses and figure them out from there. Really, as of right now, the only bosses confirmed for Icecrown are the Lich King and Syndragosa.