The Insidious / Sinister Crossover is the untitled crossover between the successful horror franchises, Sinister and Insidious. Producer Jason Blum claims that a crossover between horror movie franchises Insidious and Sinister is likely to happen at some point in the future, as it is already at early production.
It is most likely the film may arrive during the 2020 - 2021 mark.
During an interview with CinePop for The Last Key, Blum had the following to say when asked if we could ever see something like an Insidious / Sinister crossover happen:
"I hope so, I want to. We almost did 'Insidious' and 'Sinister' and I still feel like we might do that, so I think so. I think we're going to cross our worlds at some point. I don't know how yet, but we're going to try."
In addition to dropping that bombshell, Blum goes on to talk about the future of the Insidious franchise, confirming that there will be a sixth installment (provided The Last Key earns at the box office), and possibly even a seventh, in order to extend the series past the six-film run of Paranormal Activity.