Obviously, at the end of X-Men Apocalypse, we assumed we might see Mr.Sinister in Logan, but those rumors have been squashed. What we do know is, Mr. Sinister will more than likely be in the next X-Men film (X-Men Supernova). Since we are pretty certain they are doing the Dark Phoenix Saga, it makes sense.
Here’s what producer Simon Kinberg has to say about the sinister Nathaniel Essex:
“The short answer is yes,” Kinberg said when asked if Sinister will be making any big screen appearances in future. “We’d love to see Sinister. I think he is one of the great untapped villains in the X-Men universe, and we do have plans to introduce him into the world.”
Interestingly, Bryan Cranston has expressed interest in playing the role.