World
* Northrend is Huge. It is larger than Outland by a couple of zones, and some of the zones in Northrend are bigger than the largest zone in Outland. (Source)
* The mounts available to buy in Wrath will probably be able to take passengers. These mounts will also work in the old world (Provided they are land mounts), so players can give low-level characters a ride! The new mounts will also be slightly faster, around the speed of the Armored Netherdrakes. (Source)
* We're not sure if that will be available from the start but one of the ideas is to give the players new mounts they can buy and allow these new mounts to be available for passengers. (Source)
* Trainers and Auction houses will remain in the "Old World" (Source)
* Dalaran wil be in Nothern/Central Northrend, near the final zones (Source)
* The Ashbringer lore will feature heavily in Wrath (Source)
* More details on Northrend and Vehicles in Part 1 and Part 2
Professions
* Blacksmithing may be able to put Gem slots on items that didn't have them before (Source)
* All professions will give players something powerful specific to them, similar to the Epic weapons that weaponsmiths can make just for themselves (Source)
* A new metal ore found in Northrend is Cobalt. (Source)
* The new cloth in Northrend is called Frostweave. (Source)
* The way inscription is going to work is you'll have a series of mats that you need to do and then you'll create a scroll that will actually do the buff of the spell in question. Each scroll will have a specific use, so you won't create a generic scroll, it'll be a special scroll that will upgrade this fireball to do this type of thing. Right now we're still trying to make sure we've got that kind of mechanic down. That's actually most of the work. Most of the work is figuring out how that all works, what the materials are, how that comes together, and once we have that, then figuring out what the individual spells are and what the individual spells are and what the effects are going to be is going to be relatively easy. (Source)
* More details on Inscription in Part 2
PvP
* Lake Wintergrasp will have daily quests, and there will probably be a buff that effects the entire continent, as well as rewards from all dungeons similar to the Spirit Shards players can currently get from the Auchindoun instances when their faction controls the area. (Source)
* There will probably be two new Arenas in Wrath, one set in Dalaran, one in Orgrimmar Arena (Source)
Raids & Dungeons
* In Wyrmrest Temple there's a raid instance similar to Onyxia's Lair where it's a small raid instance with a single encounter in the Chamber of Aspects. We plan to put a raid encounter in there and let you take part in that and initially we plan to go with one raid encounter, but if we want to expand the space and introduce other dragon flights we can do that through the Chamber of Aspects. (Source)
* A raid encounter in the Nexus will let players free drakes and then fight on their back, allowing them to use their abilities. Bronze, Green, and Red drakes will be available and each one of them will have his own set of abilities. The boss fight is tuned around the abilities of the drakes and players will be able to pick any combination (e.g. 3 Green, 1 Bronze, and 4 Red). There's a boss fight that has lots of adds in it, and one of [the drakes] can apply this buff to a bunch of adds while another one can basically consume the buff and get health back from all of it and also assume a tanking role. So your tank is then healing himself based off of this debuff that another one is applying to everyone. (Source)
* Developpers think they didn't reward PvE enough in the Burning Crusade, and will try to change that in WotLK. (Source)
* Heroic dungeons weren't rewarding enough in BC, Wrath of the Lich King will change that and make player feel that Heroic instances have their own tier of loot instead of a few additions to the normal loot table. Expanding the Heroic Badge system will be a major step to achieve this. (Source)
* The Arthas storyline will play out through the patches as well. So Arthas doesn't die in shipping Wrath of the Lich King. Arthas will die in a content patch. (Source)
* PvE ladders on the official armory are possible in the future (Source)
* More details on Raid & Dungeons in Part 1
Death Knights
* Changing runes won't be as prohibitive as talent speccing or anything like that, but at the same time, it won't be so fluid so that you're doing it between fights. We're going to hit some sweet spot between those two. (Source)
* Death Knights aren't restricted to swords, they can also uses maces and axes and dual-wield their 1-hand version. Obviously, they can't use a shield. (Source)
* Using a 2-hand weapon or dual-wielding won't change anything to the amount of runes (6) you can use. (Source)
* Death Knights will start off in a floating necropolis in the Eastern Plaguelands, much like Naxxramas in its current location. They will then go on to level in a dedicated area East of Tyr's Hand and the Noxious Glade, where they will learn more about the background of Death Knights. (Source)
* A few more DK abilities
Blood Presence - DPS. Increases DPS and heals the DK slightly when attacked. (Source)
Blood Strike - Does an amount of damage based on how many diseases are on the target. (Source)
Blade Strike - Applies disease to the target in addition to doing damage. (Source)
Mind Freeze - Interrupts spell casting (Source)
* More details on Death Knights in Part 1
Patch 2.5 ?
* "We just released 2.4.2 on the PTR [public test realm] last week and that's just kind of a minor bug fix patch with a handful of small adjustments. 2.4.0 does represent kind of the last content patch for Burning Crusade and for WoW before Wrath of the Lich King comes out, and so we are talking about doing something in between when 2.4.2 comes out and when Wrath of the Lich King comes out but haven't decided exactly what that is or when that's going to come out. It's only a possibility at this point." (Source)
* "There will be no event to open the route to Northrend like AQ; the day of the expansion release, players can go straight into Northrend. However, a month or 2 in advance there will possibly be a large patch, similar to pre TBC. Players will get hints of why they will have to go to Northrend in this peroid, and this patch will possibly feature new talent trees and class changes." (Source)
* "Blizzard are planning to bring out cool new items for players to spend all their money on, BEFORE Wrath comes out." (Source)