After the fallout of the Blizzard Immortal announcement, it is now being reported that Blizzard were set to close the show with a Diablo 4 reveal.
A report by Kotaku says that the reveal was apparently set to take place after the Diablo Immortal announcement. The announcement was set to take place with Blizzard co-founder Allan Adham revealing that Diablo 4 was in the works, but not ready to be shown yet.
The plan to reveal Diablo 4 at Blizzcon was apparently changed within the last couple of weeks, mainly because the Diablo team was worried about revealing the game at this early stage. The game has reportedly taken two wildly different directions under two different Directors.