In a post on ResetEra, Jason Schreier noted that he knows what is being teased but doesn't want to reveal it because "it's a good one".
A recent teaser tweet by show host Geoff Keighley could end up being for the action RPG looter's second expansion after all.
Fergusson said that, "After five years of driving the Diablo franchise forward," it's time to step away and "see what's next."
Blizzard's action RPG will see its latest season going live on the same day, bringing new content, activities and improvements.
While the live-service elements are an issue for now, Blizzard believes that there is "opportunity there" for Diablo 4 on Switch 2.
Blizzard Entertainment also confirms that the action RPG's next expansion will launch next year, complete with a new ranking system.
Diablo franchise general manager Rod Fergusson also spoke about only announcing new expansions when the studio is ready.
Along with Microsoft's catalogue, the rumour also alleges that Bandai Namco's Elden Ring and Tekken 8 are coming to the console.
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Diablo franchise boss Rod Fergusson says the expansion won't just feel like a "single moment in time" for current owners.
"I don't want it to be, like, the third level that you cut before you launched," says Microsoft Gaming CEO Phil Spencer.
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Kurast Undercity is also more rewarding with more random items, double the Gold drops, and at least one guaranteed Legendary item.
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Some new end-game activities and a powerful class add to the solid base game, even if the story and characters leave much to be desired.
Blizzard Entertainment's action RPG received its first paid expansion recently, seeing widespread acclaim from critics.
There's no ETA on the enhancement, with series GM Rod Fergusson stating that further details will come at "a later date."