*UPDATE*
So, i just got off the phone with my friend who works at Blizzard Co. Here are some details of the new content coming about.
1. Apparently there will be a new act 6 boss named Baalia, she is the off-spring off Baal (act 5 boss) and Diablo's sister (Gweneth) the new boss name is Baalia Act6
2. There will be 10 new quests to complete in Act 6. It will be the largest act in the entire game roughly 2x the size of other acts.
3. There will also be an Act 7 which is the underworld, there will be 2 quests in this act and you face a new super boss who is actually above Baal and Diablo
4. In all these acts there will be all new monsters as well. With new types of spells and physical damage + attacks.
Char Improvements
1. Barbarian will now have the ability to do a magic damage whirlwind, they are adding new helms for him as well and gloves that are specially designed for barbarian class
2. The "Bash" skill is being completely reworked to where it is now a charge attack and covers a good distance.
3. The warcry skill is apparently going to be doing 2x as much damage with adding a new synergy to it.
4. Sorceress will now have a new runeword called "element" that could be made in 2 socket orbs with it being Ist/Jah It will roll 1-4 skill, 20-40% Ice/Fire/or Light damage, +1-4 energy sheild, 5-10 fcr, and either +1, or +2, or +3 fire/light/cold mastery (a rollers dream here)
Charm Improvements
Grand Charms will now be customizable. +50 life skillers will be attainable and could be found. You can also roll modifiers to the actual charm like +% to cold, light, fire, magic damage
That's all i got for now guys!