The system designs team were bombarded with questions during the 1-hour Twitter chat yesterday. Many questions were focused around the new class, talent and mastery system, and a lot of blurry questions regarding talents were answered.
We find out that it won't be any real class specific quests for Cataclysm, but that class-specific dungeon quests for everyone at levels 20 and 50.
- "It’s very expensive to create class-specific quests given the literally thousands of new quests we are already adding for Cataclysm; however, we are going to have class-specific dungeon quests for everyone at levels 20 and 50. These won’t be as involved as, say, the old Benediction quest line, but they will give you a way to get some blue loot that isn’t otherwise available," says Blizzard.
Blizzard are also trying to move away from having purely PvP or purely PvE talents.
- "This is almost impossible to “fix.” With the nature of talents min/max will always be possible. That said, we’re trying to move away from having purely PvP or purely PvE talents as much as possible, which will make the pure PvP specializations less painful to play in PvE and vice versa."
All these changes will be added into Wrath of the Lich King even before the release of Cataclysm, just like it went down with The Burning Crusade and Wrath of the Lich King.
Follow the link below to see all the other questions and answers.

Links
WorldofWarCraft.com - Full Q&A thread