I’m pretty sure they will try to delay the release of D4 as long they could like they are doing with Immortal. Blizzard has no other games on the horizon and with most of their current games either dead or dying, they will be biding their time until they think of the next warcraft themed hit game. Shareholders will be happy that people are getting hyped for a new game and when revenue drops from their other games and shareholders start to worry, only then comes D4.
Blizzard has no other games on the horizon? OVW 2 , wow shadow lands event to the summer game festival, and there are job posting for other 2 games mobiles Unannounced Project and we don't konw if leaked Diablo 2 resurrect is real or fake .
another Lead artist for another blizzard game Unannounced project https://careers.blizzard.com/en-us/openings/oSIFbfwa
Not really surprise If warcraft franchise take mobile title after DI.