A lot of things are going to change in Diablo 3: Reaper of Souls and one of these will be the new Paragon 2.0 system. The system was implemented to provide players with some form of tangible benefit for killing lots of monsters even if they were unlucky with items loot.
The first thing that is going to change in Paragon 2.0 is the current cap, which will be completely removed. The next thing worth mentioning is the account-wide Paragon level change. In order to help players experience all in-game classes, without worrying about the experience waste, Blizzard will make paragon levels account wide, especially since one of the most expected feature from Reaper of Souls will be the new Crusader class and a lot of re-rolls are expected.
When earning a Paragon level in the new system you will receive a Paragon point. Level 1 will give you a point that can be spent in a Core stat (Str, Int, Dex, Vit), level 2 will give you a point in the Offensive category, level 3 for Defense and level 4 will get you a Utility (Adventure) point. All Paragon levels past that will follow the same patern.
Beside Paragon 2.0 and Loot 2.0 systems, the closure of Auction House, it seems like one of the most beloved bosses will be back. You know which one? The Cow King. For the moment nothing was officially confirmed, but in a recent data mined video, Maul05 presented some of the new monsters and bosses that may appear in Diablo 3: Reaper of Souls including the Cow King.
NOTE: SPOILER ALERT VIDEO