I'm afraid they don't want to show Nathaniel Essex as of yet. They already killed Shaw and Apocalypse, and Trask in jail. There is virtually no way they'll come back. But Nathaniel Essex was "referenced" in the post-credits scene of X-Men: Apocalypse, where it is seen to be the precursor of Alkali-Transigen in making the X-23 children in Logan. However, the character himself seems to have never appeared on screen. It is, however, very likely he will appear in future X-Men movies. Deadpool 2 could be one of those, despite it seems unlikely. X-Men: Dark Phoenix, he could appear only in a cameo. The New Mutants could also be home to him, but still unlikely. The most likely is proabably Gambit, because of it's connections.
However, I think that the biggest work for the franchise is to crossover with the MCU. I imagine a moment of X-Men and Avengers crossover like this: