Blizzard has updated their Under Development page to include more information on the upcoming 2.4 patch.

Sunwell Isle - A new area located north of Silvermoon City
- Sunwell Plateau - A high-level 25-player instance featuring six bosses
- Magister's Terrace - A high-level 5-player instance
- New Reputation - The Shattered Sun Offensive is Shattrath City's answer to Kael'thas's operations in the Sunwell; it is comprised of the combined forces of the Aldor and the Scryers, led by the naaru.

Item Improvements
- New Heroic badge rewards
- Some PvP rewards now obtainable through PvE content

You can find even more information here.