WotLK: Spoilers Ahead, Read At Own Risk

This post is about an upcoming quest-line in Northrend that is hotly discussed on the forums at present. If you wish to remain blissfully ignorant as to quests, content, lore-twists, and all things Wrath of the Lich King, do not read any further.
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Currently in WotLK, there is a very long quest-line for the mid-70's that, by all accounts, is the epitome of epic. It pulls together all sorts of storylines and factional heroes for a showdown to rock the entirety of Northrend. If that description doesn't get the juices flowing, I don't know what will.

Factional heroes Fordragon and Saurfang are the leaders of the Alliance and Horde camps at the gates of Icecrown Citadel. The gate is named Angrathar the Wrath Gate - it is forged using the blood of an Old God. I do not have details on the quests leading up to the monumental world-changing event about which I am about to delve, but I have been assured that it is long, involved, and lore-rich.

The camps are gearing for an assault on Icecrown. Fordragon calls Arthas out, a battle ensues, and, well... here's a link to the proceedings:
SPOILER-RICH EPICNESS

Now, here's where I go from excited to floored. The Royal Apothecary Society was working in concert with Varimathras - simultaneous to all the hubbub at the Wrath Gate, Varimathras made a bid to overthrow the leadership in the Undercity. Here's some preliminary quest text from Wowwiki:

The Battle For The Undercity

As the combined Horde and Alliance forces began their assault upon Angrathar the Wrath Gate, an uprising broke out in the Undercity. Varimathras and hordes of his demonic brethren overran the city, slaying all those who would not submit to their dark rule. Sylvanas herself was nearly killed in the coup, but managed to escape with a number of loyalists and fled to Orgrimmar. Determined not to allow the Dreadlords a foothold in Horde territory, Thrall and Sylvanas planned an immediate counterattack. In the midst of their planning, Jaina Proudmoore arrived with terrible news: in the wake of Bolvar Fordragon's death, Varian Wrynn had ordered an assault on the Undercity, not to remove the Dreadlords, but as the first strike in a new war against the Horde.

Sylvanas returned to the Undercity at the head of a Horde army,
determined to retake her city. Along with Thrall and Vol'jin, she led the assault into Undercity itself, a cry for her people upon her lips. In the Throne Room, Sylvanas fought and finally slew Varimathras, retaking her Throne at a cost not yet forseen.

The quest info above appears to be from a Horde P.O.V., but rest assured, there's an Alliance component. Wrynn and I believe Lady Proudmoore charge into Undercity at the head of an Alliance contingent to cause general havoc for the Horde.

Now, I've always said that one thing that I've wanted to do more of is raid capital cities. What did Blizzard do? Take note of the bolded text in the above (emphasis added by me). They re-installed the King of Stormwind, made him a warhawk, and had him declare all-out war on the Horde, starting with a raid on a capital city. The quest has players fighting through a phased Undercity alongside several Alliance heroes. It's a whole new world, and that world involves epic quest-sanctioned raids on the Undercity.

I, for one, welcome our new bloodthirsty overlords.

I snipped most of this information from this disucssion thread on Maintankadin, for any who are interested.

EDIT: For more on the above proceedings, check out Alex Ziebart's WoWInsider article.