Blizzard should just officially acknowledge the fact that Diablo 4 is in the works in order to appease the enraged fans. Kotaku's sources claim that Diablo 4 has been in the works since late 2013 and the game changed direction in 2016. In its early stages, Diablo 4 looked like Dark Souls, but the vision changed to a more traditional isometric ARPG with dark art style.
https://www.notebookcheck.net/Diablo-4-originally-designed-as-a-Dark-Souls-3rd-person-game-new-project-sticks-to-isometric-view-and-dark-look.366006.0.html