A Blizzard job listing for an "Art Director, Unannounced Project" strongly suggests that something new is happening in the land of Diablo. How can I tell? Because directly underneath "Unannounced Project," it says, "Diablo."
"Blizzard Entertainment, the developer of the most epic games in the world, is seeking an exceptionally skilled and passionate art director to help develop Blizzard’s next hit game!" the listing states. "Work alongside a team of the best artists, engineers and designers on the planet and enjoy the support of a company whose culture is centered on collaborative game development."
The successful applicant will have at least ten years experience "crafting videogame art," and five years as a lead artist or art director. Other prerequisites include "incredible communications and interpersonal skills," experience handling a large staff, proficiency with various 2D and 3D applications, and the ability to crack the whip and drop the hammer as needed. "A passion for games with a deep understanding of the Diablo franchise" is listed as a plus. See, there's that whole Diablo thing again.
So yes, I'm definitely putting my money on Diablo here. We'll keep our ears to the ground.