The news broke earlier today via an article from Deadline. Morgan Creek is reportedly working on a reboot of The Exorcist.
"Current Morgan Creek projects include Stay Tuned at AMC, with a planned theatrical reboot of The Exorcist in the works for 2021."
With the iconic franchise recently finding success on TV with the brilliant, yet short lived, The Exorcist TV Series it comes as no surprise there is more on the way. The TV Series had a fantastic response from fans, many of which (myself included) are still hoping for a third season. Of course like many other great TV shows nowadays, it was cancelled.
The success of the show has definitely reminded producers that horror fans still have a lot of love for The Exorcist, and are probably longing for another film. The last being 2005's Dominion: Prequel to The Exorcist, which unfoetunately was nothing special. It'll be interesting to see what they do as I think there's a lot they wouldn't be able to get into the film nowadays.
There's no other details at the moment. We will update as soon as we know.