Blizzard quietly confirmed work on a new Diablo content through a job listing on its website simply titled: Dungeon Artist, Diablo.
There is no other news about the new game at this time, aside from this confirmation that it's being worked on and some flavortext in the listing to get you hyped to work on the project, "We're working on a new, unannounced Diablo project. Are you a skilled Dungeon Artist? Come work with us, and together we will build something exceptional."
But, if you happen to be a 3D environmental artist, Blizzard's hiring!
The Job listing can be reached here: https://careers.blizzard.com/en-us/openings/oNiH7fwD