I'd like to see Icecrown Citadel be a massive army-based thing. The forces of the Horde, Alliance, Argent Crusade, and Ebon Blade band together to lay a massive assault on the citadel. Each boss you defeat allows your raid to go deeper into IC to the furthest base camp (the base camp is under constant assault by weak elite undead to show the constant battle raging)
The first few fights could involve the entire raid mounted on argent warhorses with their normal abilities. (except maybe a taunt or something) Minimal healing, just pure dps until you reach the citadel interior.
I figure there are at least two potential things for Saurfang to be a boss. In the first case, he could basically have his soul stuffed into a massive saronite construct that engages in rough rape with raids. The other is having him be part of the Arthas fight, detailed later.
The Arthas fight simply wouldn't be any kind of epic if it wasn't an army-sized battle. Most of the major lore figures being there like Thrall, Sylvanas, Jaina, Tirion... The fight should largely revolve around veritable hordes of undead swarming in from every corner, dead soldiers being raised right on the spot. One phase in the fight, possibly the final phase, would involve Arthas jamming Frostmourne into the ground and releasing its entire energy. All the souls that he has stolen are bound to his will and attack the raid in waves. Small non-elite nameless soldiers, elite lieutenants and captains. Saurfang the Yonger, King Teranas Menethil could be big mini-bosses. A shade of Illidan could also be present. The injury was a contributing factor in the descent of Illidan into madness, it isn't a longshot to think that part of his soul might have been taken. Mostly for the sake of fighting Illidan in a way again anyway.