Blizzard missed an opportunity to mitigate the backlash to their BlizzCon announcement of Diablo: Immortal for mobile if an unconfirmed rumor on Kotaku is correct in saying that the company pulled plans to tease Diablo 4 at BlizzCon at the last minute. They attribute this to "two people familiar with Blizzard’s plans" who say the mobile announcement was to conclude with the news that a proper sequel in the action/RPG series is in development, but not yet ready to show. They describe the no comment they got back from Blizzard in an unusual way: "Blizzard said it did not immediately have comment on this story." The Diablo: Immortal announcement generated controversy, but this report recalls that Diablo III was not without its own issues. The game launched with an online auction house that was very unpopular, eventually provoking a major post-release rework amid shakeups atop the development team. From Kotaku's account, it sounds like they are still a little shell-shocked from that misstep, which may be why they would slow-walk an announcement:

The reactions could have been very different. Blizzard changed its BlizzCon plans for Diablo at some point in the last couple of weeks, those people familiar with goings-on at Blizzard said. One of those people told me that the Diablo team wasn’t yet ready to commit to an announcement, as Diablo 4 has changed drastically over the past four years and may continue to change further. (We’ve heard it’s gone through at least two different iterations under different directors.)