Fourth Difficulty
      

  I was in a meeting with Jay and Wyatt earlier (about something completely different), and Wyatt expressed specifically that giving players some sort of end-game that doesn't involve grinding areas or bosses is something that keeps him up at night. It's a real problem, and it needs a real solution. It's also very much in the minds of our designers..
      

http://www.blizzblues.com/us/fourth-difficulty-26262771716.html