Diablo III is arguably the weakest link in Blizzard's current portfolio, and, although the company is not really pressured by upcoming Korean MMOARPGs, it at least owes it to the fans to hype things up for the Diablo franchise once again. Blizzard acknowledged the existence of multiple Diablo-inspired projects already in development, some of these being scheduled for a reveal at Blizz Con this year.
https://www.notebookcheck.net/Blizzard-has-multiple-Diablo-projects-in-the-pipeline.321278.0.html