According to Deadline: Blumhouse Productions is moving forward with 'Sinister 2' with plans to turn it into a franchise. Plot details are unclear at this time or who will direct the sequel, but it appears Scott Derrickson and C. Robert Cargill will be back in some capacity as they wrote the original film.
Original film followed: A true-crime writer finds a cache of 8mm home movies films that suggest the murder he is currently researching is the work of a serial killer whose career dates back to the 1960s..
(Source: Horror-Movies.ca)