Getting the director of the second movie to finish off the trilogy would certainly be an interesting move, and it’s happened with several other franchises in recent years. Paul Greengrass with Bourne 2/3 and Matt Reeves with these last two Apes movies both come to mind.

I feel like it almost certainly won’t be JJ. He looked and sounded exhausted by the end of TFA, and IX will have an even more compressed schedule if they really are going to have this in theaters by Memorial Day weekend of 2019. He was going to take a break after Star Trek Into Darkness and spend more time with his family when Kennedy offered him VII. Last I heard, he was going to direct that miniseries of The Nix with Meryl Streep. Checking “direct a Star Wars movie” off his bucket list was probably enough for him.

As for why Trevorrow is leaving, I feel like Book of Henry isn’t the reason. For all we know, this might have been more his decision than Kennedy’s.