[SPOILERS for Insidious: Chapters 1-3 ahead.]
Horror movie franchises are nearly as difficult to kill as horror movie villains, as evidenced by the fact that new Friday the 13th, Halloween, and The Ring movies are currently in the works. Meanwhile, Universal Pictures and Blumhouse are moving forward with a fourth installment in the Insidious franchise and have now scheduled Insidious: Chapter 4 on a theatrical release date that the studios claimed for an "Untitled Blumhouse Productions Project" earlier this year.
The Insidious movie franchise was co-created by Leigh Whannell and James Wan, who wrote and directed the first two films, respectively. Insidious and Insidious: Chapter 2 together form a two-part narrative about the Lambert family and the demonic entity that had plagued father Josh Lambert (Patrick Wilson) ever since he was a child. Insidious: Chapter 3, which Whannell both wrote and directed, took place before the events of the previous installments and examined a different case that parapsychologist Elise Rainier (Lin Shaye) worked on - one that led to her initial encounter with the same demon that would eventually take her life during the events of the first Insidious.
Insidious: Chapter 4 is also being written by Whannell and produced by Wan, but with Adam Robitel taking over as the director for this "chapter". Shaye is confirmed to reprise her role as Elise in the film, though that doesn't really narrow down where Chapter 4 takes place in the Insidious movie timeline. Although it's possible that the fourth Insidious will be set between the events of Chapter 3 and the original Insidious movie, it could also take place after the events of Chapter 2 - which concluded with Elise now being a (friendly) ghost, still helping the ghost hunters Tucker (Angus Sampson) and Specs (Whannell) in their ongoing battles against demonic forces.
Universal/Blumhouse has scheduled Insidious: Chapter 4 to open in theaters on October 20th next year, where it will serve as counter-programming to Ben Affleck's historical crime drama/thriller Live By Night. Blumhouse had released a new Paranormal Activity movie in theaters around Halloween time for most of the past 5-6 years. However, now that said found-footage horror movie series has finished its run, Blumhouse will be using Ouija 2 and the fourth Insidious movie to fill that "hole" left behind by the Paranormal Activity franchise in October in 2016 and 2017, respectively.
While Insidious: Chapter 2 split critics with regard to how it dives much deeper into the first installment's mythology (read: the mythos of "The Further") than most anyone expected, Chapter 3 was overall better-received and is generally regarded to be a perfectly serviceable horror movie that brings the Insidious series full-circle in a thematically satisfying fashion. It's difficult to see how Insidious: Chapter 4 could be about much more than keeping the Insidious brand going, for that reason. Then again, Robitel's previous directorial effort (The Taking of Deborah Logan) was a pretty well-received found-footage horror film on its own terms, so perhaps there's hope for the fourth Insidious series installment yet.
Insidious: Chapter 4 opens in U.S. theaters on October 20th, 2017.
Source: Universal Pictures/Blumhouse