Let's be honest here, there are few more prominant mortal characters in Warcraft right now than Tirion Fordring. He's gone from a retired former Paladin who lost his family and watched as his son was corrupted and killed to the dude who's risen above the strife between the races and is taking the fight to Arthas. He's honourable, impartial and even-handed to a fault. Over the course of the Expansion he's brought diverse races and classes into the ranks of the Argent Crusade and succeeded in quelling much of the antagonism between the major factions. It's likely were it not for Garrosh Hellscream, Fordring would be able to forge a cease-fire between Thrall and Varian Wrynn. He also currently wields the Ashbringer, a more badass weapon you're not likely to see, and urged the acceptance of Deathknights into the fold of the Alliance and Horde.
Fordring has become a rallying standard when the Horde and Alliance have a common enemy, and as such will continue to be an obstacle when the game seeks to foster conflict between the races as seen in Cataclysm. He would also be the first target for any enemy seeking greater dominance over Azeroth. The character is starting to play a more central role in end-game lore than any of the major faction leaders. In short, this guy has to go.
One Last Hurrah for Arthas?
With all that's happened over the past few (in-game) months the power and evil of the Lich King is getting lost in the shuffle. We know that he destroy our souls with one spell but even now he's too timid in reacting to our encroachments into Icecrown. He should be planning something special to negate the advantages Tirion brings to the Crusade. And the figure of the Lich King is powerful enough to warrant taking out some big names as we bring him down. Fordring, as a neutral, well-loved and big name character, is a prime candidate.
There are of course more than a few ways in which Arthas may blunt the effectiveness of Fordring. Here are a few I can think of off the top of my head.
Poison his steed, Mirador. Defile the tomb of Uther Lightbringer. Systematically turn a large number of his Crusade. He may be able to take them being killed, but corruption from within would tear the Crusade apart. Bartholemew, Tyrosus and the Crusaders at the Tourney are contenders. Reveal his estranged wife Karandra as a member of the Cult of the Damned. Raise his son Taelen as an Ghoul or even a Deathknight to lead the Undead vangard against the Argent Crusade.
Without a doubt, Arthas will be dispatched in 3.3 either through elimination or redemption. It also appears that he has put plans in motion to counter the Alliance and Horde specifically by the enforced turning of two of their champions. Surely, after going to so much trouble to draw out Fordring for battle he will target the main man again.
Presupposing an encounter between Arthas and Tirion the Ashbringer and Frostmourne saga's should be concluded. In so doing the backstory detailing the origin of both Runeblades should finally be fully revealed, explaining if the Ashbringer was indeed forged from the spark of a Naaru and who crafted Frostmourne. Perhaps the confrontation between these two opposing elements would cause them both to be destroyed. It might even have been a plan of the Naaru; we know that they are adept at seeing the bigger picture and planning ahead.
The Aftermath - Disbanding the Argent Crusade, Inspiring New Paladins
With the death of Fordring and the supposed end of the Lich King's Undead threat the disparate groups which make up the Argent Crusade should slowly drift apart. Recall that the Crusade was conceived as a union of the Argent Dawn and the Order of the Silver Hand, the latter of which is an Alliance group that has set aside the issues around working with the Horde to combat a common foe. The Argent Dawn may well continue as a neutral faction in the future, but greatly diminished in power and influence.
The memory of Fordring would serve as an inspiration for new Paladins that transcended boundaries of race, especially if supported by the major moderate figures of the Horde such as Thrall and Saurfang. If handled correctly this could inspire the Tauren to feel comfortable embracing the Light, just as they embrace nature now.
Blood Knights and the Order of the Silver Hand could feature as two new major PvP factions in the Cataclysm world, both seeking to discover the origins of Light in the Titan Parthenon. Alternatively, the Order could be a neutral class faction similar to the Ebon Blade or Cenarion Circle, but I think divorcing it that far from the Alliance would be a mistake.
Other Lore Potential: Garrosh, Daval Prestor and the Old Gods (Spoilers!)
How has Garrosh changed from a whiny crybaby to the Warchief-in-Waiting? We could perhaps justify it in a retcon (otherwise known as OMG Comic!), but perhaps simply using the available tools would get the job done. Recall that what may appear to be a series of unconnected threats is essentially the fight for dominance of two overarching forces: the Titan Pantheon and Old Gods.
As seen at Blizzcon, Horde fortifications are being reinforced with a curious black iron which should seem familiar: it's Saronite. There's only one source of the dangerous ore in the world and the mining of it leads to inevitable madness with prolonged exposure because of the whisperings of the Old Gods. Surely only a fool would expose themselves and others to their influence, and not even Garrosh would support such an action? However, perhaps Garrosh came into contact with Saronite very early and the Old Gods, sensing a weak and malleable mind, chose to corrupt him. This would certainly account for his fast change of outlook, aggression, and erratic temperament.
The Dragon Aspect Deathwing will return in Cataclysm, and may reappear as Lord Daval Prestor. It was never made clear if his cover had been blown or if only Rhonin and Krasus know his true identity, but he was once an ally of the leader of Gilneas, Genn Greymane. Prestor may once again wield power and influence amongst the Alliance, continuing the plans of the Old Gods on Azeroth by sowing the seeds of conflict between the Alliance and Horde. The unmasking of Lord Prestor could in fact be a major event in WoW before the Deathwing raid instances are released, recapturing the epic feel of a similar quest now removed.
With 3.3 likely due some time before the new year a protracted release date for Cataclysm seems unlikely. As Dylan once said, 'Time's, they are a'changing', and 4.0 will see the biggest upheaval in the games' history. I just hope that the lore surrounding the events is as compelling as it needs to be, and isn't all farmed out to the Comic Series.