Update 07/01, 8pm GMT: Jeff Ross' estimation was pretty off. His source, the now-defunct Gamestat, tracked how many people played it, but how many actually bought it. This would therefore include people who played through PS Plus, rentals, used copies or borrowing from a friend. (Thanks, Push Sqaure)
Original Report 05/01: Ex-Sony Bend director Jeff Ross has revealed on Twitter that Days Gone sold a whopping 8 million copies in just over a year and a half after the game launched. He also reveals that Days Gone has had a similarly impressive outing on Steam, having sold over a million copies since its PC release back in May last year.
This comes shortly after the news that Ghost of Tsushima also recently passed the 8 million sales milestone, a game that had a significantly better critical reception than Days Gone. According to Ross, studio management made him and others feel like Days Gone was a "big disappointment" and is likely using Ghost of Tsushima's similar sales to try and prove that Days Gone was, in fact, a success.
It was revealed in an article from Bloomberg reporter Jason Schreier last April that Days Gone wouldn't be getting a sequel despite commercial success, leading to criticism from many that Sony's obsession with critically acclaimed blockbusters is what led to Days Gone 2's cancellation. If Jeff Ross is to be believed and his numbers are accurate, it would definitely back up that theory.
It's not like there isn't support for Days Gone 2 either. After the cancellation of a sequel was confirmed, a petition for Days Gone 2 on Change.org managed to amass over 100,000 signatures, a feat which Ross acknowledged on Twitter. Jeff Ross himself was also keen on a sequel, sharing what features Days Gone 2 would have had closely after news of the cancellation broke. This included a secondary co-op mode in which players would be able to try to survive a zombie apocalypse with friends.
Instead of Days Gone 2, Sony bend is now working on a "great new concept" for PlayStation 5, which has already been revealed to be a brand new open-world IP that is building on the "open-world systems" from Days Gone.
This news seems to have transpired due to the likelihood that Ross still feels a bit disheartened by the cancellation of Days Gone 2, but if over 8 million sales in a year and a half isn't enough for Sony to greenlight a sequel, who can blame him?