The first "content" patch for ROS, which will include ladders, is due in a few months. There has also always been speculation that there would be two expansions to Diablo 3. In light of that, I looked at the seven character classes in D2 and the six in D3, including followers, and created the following table. Read down a column to the grey cell, then across the row for each character. It looks like each character class from D2 has been included, at least partially, in D3.

What would the seventh character class be?