According to Wccftech Blizzard has long-term plans for Diablo 4:
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Thanks Couchpotato!Blizzard Has A 10-Year Plan For Diablo IV According To Series General Manager
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"We're here for the long haul," Fergusson said. "We've been doing long-range planning recently. And I've created a roadmap - a 10-year roadmap...it was actually a 12-year [roadmap] - I can see this, this, this and this and all these different things that we can do, [which] is really inspiring. And it's really exciting. We're focused on what players want...I can't tell you much more than that."
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