Blizzard has opened a teaser site for a Diablo 3-related project, titled "Reaper of Souls." Though the site is bare-bones for now, it certainly implies some kind of Diablo announcement on the horizon.
The Reaper of Souls site simply says, "Death, at last, shall spread its wings over all," apparently a passage from the Book of Tyrael.
We know that a Diablo 3 expansion has been in development since at least this time last year, and Blizzard has mentioned some kind of announcement being readied for Gamescom. Whatever the Reaper of Souls might be, we'll know soon enough, and then have to see what that means for the impending console versions.