Job listings are generally a reliable point from which to speculate on, often long before a publisher ever plans to actually announce the game it's hiring for. That's what's been happening at least with Blizzard and Diablo.
Almost two years ago, Blizzard started taking applications for a game director who could take Diablo and "lead the series into the future." And around BlizzCon last year, multiple positions related to Diablo were listed as employment opportunities.
Today, there's an opening for a dungeon artist. What this means is there's going to be more Diablo at some point in time in the future. Not that there's ever been any doubt about a future for Diablo, given that it's easily one of the company's most iconic and successful properties.
The description makes it clear something new is happening: "The minions of Hell are growing stronger... We're working on a new, unannounced Diablo project. The ideal candidate works well in an environment of peers who are passionate about working on the dark gothic world of Diablo, making great games, killing millions of monsters and getting loot."
Simply put, a reminder to everyone crazy enough to think Diablo is dead that Diablo isn't dead. It's just anyone's guess whether the next Diablo project materializes this year, or two decades from now.