“Blizzard Entertainment is seeking a game director with outstanding communications skills, proven experience in creative direction, strong ability in system design, and a stellar track record of shipping AAA games to lead the Diablo series into the future.”
The phrase “Lead the Diablo series into the future” certainly implies a new Diablo game, although that has yet to be confirmed by the company. Blizzard has not given any details on what exactly this means yet. Considering how quiet they are being, it probably means another full game, rather than a DLC or something of that nature.
The opening could be speculated due to the recent departure of previous game director Jay Wilson, who parted ways after over a decade with the company. If you want to apply or read the full details, you can see the job opening here.