Earlier this month, Blizzard confirmed some unfortunate, but otherwise to-be-expected, news. Neither Diablo 4 nor Overwatch 2 are set to release in 2021, and while many more seemed to focus in on Overwatch 2, a lot of fans were seemingly disappointed by this confirmation. Overwatch 2 itself may have experienced some type of delay, but being upset over Diablo 4 not releasing this year seems to stem from one important factor: unmanaged expectations.
Very little is known about Diablo 4, though Blizzcon is set to reveal more information on it. As a result of this potential information pipeline and the quarterly updates, some have taken this confirmation to suggest that Diablo 4 will launch in 2022. While not necessarily impossible, it's more likely than Diablo 4 is still years away.
Blizzard Development
Video game development is a tricky situation, one that takes years and one where a single button doesn't work as a fix-all. Managing expectations comes, in part, with understanding how a particular company approaches it. For example, fans can always expected high-quality, polished experiences from Rockstar, which is why a new Grand Theft Auto or Red Dead game may not launch until the latter half of this decade, at the earliest. At the same time, Ubisoft maintains a very ordinate, collaboration-oriented development which sees it put out several games a year.
For Blizzard (not counting its Activision/Call of Duty component), it's in a similar boat to Rockstar: sometime after the later '90s and early 2000s, game releases began taking years. Expansions for World of Warcraft are a different story, but Starcraft got a sequel 12 years later, Hearthstone conception began around 2008 but wouldn't release until 2014, and Overwatch released in 2016 and its sequel may not be set until 2022 (6 years). Perhaps its worst culprit is the Diablo series: Diablo released in 1997, Diablo 2 followed rather quickly in 2000, but Diablo 3 came about 12 years later. As it stands, it's been about 9 years since the last mainline Diablo entry released.
Diablo 4 Development
Even within this, it's worth looking at what is known about Diablo development. Specifically, it should be noted that Diablo 3 was a in heavily-rumored, almost "mythical" development period for quite some time, likely beginning sometime between 2000 and 2005, before being revealed in 2008 and releasing in 2012. If this could be taken as a pattern, then 4 years after reveal would put Diablo 4 in 2023. This is, of course, without taking COVID-19 or anything else into consideration.
Diablo 4's development itself is a bit more detailed, if still less certain. After Diablo 3: The King in the North was canceled around 2013/2014, work on Diablo 4 as Project Hades began, and it would have gone in a completely different direction. Project Hades was essentially a Soulslike take on Diablo that was canceled in 2016, where work then began on Project Fenris, which by all reports, is the current form of Diablo 4. This would suggest that the core development and/or perhaps the main work load on its current form began around then, putting the game in core development for roughly 5 years.
Broad comments about it spanned from 2016-2019, where it was officially revealed at Blizzcon 2019. All of this is to say that Diablo 4 releasing in 2022 isn't impossible, but it's not likely. It's about as likely as it was for 2021. Even with the most conservative guesswork regarding Diablo 3 development, that took somewhere around 7 years and up to a full 12. With 2016 being where the current iteration of Diablo 4 began coming together, a conservative estimate would be something more like 2023. This is, again, without taking COVID-19 into consideration, which has likely impacted it to some degree (if minorly), and at the same time, it's possible some specifics are slightly off.
Regardless, expecting Diablo 4 in 2021 was a bit of a leap, and it somewhat feels that way about 2022. For now, the ball is still in Blizzard's court, but fans really shouldn't expect a Diablo 4 release date at Blizzcon. Perhaps there will be a window to aid with these expectations, but expectations should not run wild.
Diablo 4 is in development for PC, PS4, and Xbox One.