Gamespy has a quick article with guesses about the D3 expansion.

Here’s my list of what will be in it versus what should be in it.

In

• Act 5.  As long as Act 3.
• Set in Mount Arreat again (or some other location we’ve seen before)
• Hunting for Adria
• New class – melee/casting hybrid.  Likely the druid
• Level boost (10) and a few new skills per class
• New crafting mechanic that has some purpose.  Rune-like enchants.
• New item art, serving no in-game purpose

What should be in:

• Randomized maps
• Mode that doesn’t allow AH and has ladder
• Companion quests
• A social voting system to catch botters/hackers.

Knowing who is running the show, I’m not holding my breath.  D3 was certainly profitable but I doubt Blizz is calling it a success.  The RMAH experiment was a success in practical terms.  They now know how it works and how it interacts with the game.  Clearly it was a “buy to win” mode since launch.  The game also released about 6 months early, from the sheer amount of bugs in game at launch.  A profitable lessons learned event.  Can’t be mad about that I supose.