It's hard to believe The Burning Crusade came out almost ten years ago. With all the hype around the World of Warcraft movie and the upcoming Legion expansion, it's hard to deny that now would be a fantastic time for Hearthstone to explore Karazhan. For those of you who haven't ascended to face Prince Malchezaar, here's what you should expect.
"Medivh, the Last Guardian, made his home in Deadwind Pass, in the bright tower of Karazhan. Though he was the greatest wizard of his day (and humanity's intended custodian) Medivh was secretly possessed by the dark spirit of Sargeras, the Destroyer of Worlds. Through Medivh, Sargeras opened the Dark Portal and allowed the orcs to wage war upon the kingdoms of Azeroth.

As the war progressed, Medivh fought against Sargeras' control. The raging conflict within him finally drove the wizard irrevocably insane, until his childhood friend, Anduin Lothar, aided Medivh's young apprentice, Khadgar in storming Karazhan and slaying their former comrade. Since that day, a terrible curse has pervaded both the tower and the lands around it - casting a dark pall over Deadwind Pass and the region that is now known as Duskwood.

In recent years, nobles of Darkshire ventured into Deadwind Pass to investigate the blight that had settled over the region. None who entered the dark tower ever emerged."

Renown for the last Guardian of Tirisfal, our very own Medivh, Karazhan is an ancient tower in Deadwind Pass. Possessed by Sargeras, creator and leader of the Burning Legion itself and a fallen Titan, Medivh plays a crucial role in making the Warcraft world what it is today.
This is also where Echo of Medivh gets its name from as you run into an apparition of Medivh. You encounter Shadowbeasts though with a different appearence.

We'd presumably also run into the likes of Nightbane who many fans would surely appreciate.

But more importantly we'd potentially get our first Mage, Priest, Druid, or Warlock weapon in Atiesh. It might be a bit weird since Medivh is actually holding it in his Hearthstone art, but spoilers, following his death it's broken into many, many pieces. These end up in the hands of Brann Bronzebeard - who somehow loses it his portion to C'Thun - and Kel'Thuzad.

If Blizzard were to somehow incorporate some of the Warcraft lore there are many ways they could do so. In WoW, the staff can obtained by the aforementioned classes with each one varying slightly in stats. In Hearthstone there could be four different versions of it, though for clarity sake, the developers would surely want to make them obvious. In game, the cloth on the staff is green for Druids, red for Mages, white for Priests, and blue for Warlocks, however we wouldn't expect that to match up exactly in Hearthstone since the class colors do vary from title to title. The staff opens a portal to Medivh's tower of Karazhan, leaving Blizzard the opportunity to give the weapon a unique effect which plays off of that.

In Warcraft it also provides a different effect for each class. Mages increase the critical strike chance of nearby party members, Warlocks and Priests increase spell power, while Druids increase Spirit. Unfortunately it isn't really possible to piece it together, as is required in WoW, over the course of the adventure since one of the pieces is randomly dropped from one of Kel'Thuzad's minions in Naxxramas and Blizzard obviously can't just go back and change that. Not to mention the implications that would have on user experience since we literally just did that in League of Explorers.

And don't say those classes aren't allowed to have weapons! While we haven't yet seen class specific card types (secrets, weapons, etc) expand to new classes, that doesn't mean it will never happen. There's Lord Jaraxxus of course which kind of gives Warlocks one, but every single class in the game already has appropriately decorated vanilla weapon cards in the game's files. For example the card on the right is one we made when conceptualizing auras through weapons.

In addition Blizzard could explore some really cool events and locales such as The Opera Event including The Wizard of Oz, Big Bad Wolf, and Romulo and Julianne or even The Chess Event.

What excites you the most about a potential visit to Karazhan? Many are taking the latest hint, invites for a "Majestic, Marvelous, Magical Event" as more confirmation that we're likely going to visit our favorite abandoned tower.

Our sister site Wowhead has more information if you're interested.