IMO, it would be far more difficult to make movies covering Frank Herbert’s books after Dune Messiah. Especially Heretics of Dune and Chapterhouse: Dune.

While I really enjoyed Dune: Part II, it in many ways compressed the developments the middle and ending of the book. Dune: Part I was much more aligned with pacing of the book; it covered the relatively short intro of the book. I would have much preferred if Dune: Part II was split into two parts; the rise of Muad’Dib (this would introduce us to on-going developments in Dune, broader history and world-building, as well as developing Paul and Jessica’s Atreides characters) and a final movie dedicated to the narrative finale of Dune (1965).

An additional movie covering the events Dune Messiah would be a perfect fit to the “original trilogy”. A postscript movie of sorts, before starting new trilogies based on the later books.

I am not just saying this as a Dune fanboy. I spoke to several people who don’t normally watch sci-fi (let alone have an interest in Dune specifically), but who watched Dune Parts I/II and they all mentioned that Part II was difficult to follow and was a bit disjointed and that Part I had better pacing.

And no Brian Herbert and Kevin J. Anderson novels. I admit I’ve only read one (I believe it was Dune: House Atreides from 1999), but it was complete dogshit and did not feel like a Dune novel. Felt more like a generic space scifi novel.