I guess I just feel it fits Odrade's character more to have her recounting that part of the story. Using any of the Duncans will always be tricky as they're often at the centre of events and (at that point) his other memories weren't serial. I suppose an argument could be made for the last narrator to be that Duncan because he really did live (and die) through the whole thing. That actually reminds me, back when I first read Chapterhouse one of my pet theories about the two face dancers at the end was that they'd unlocked ALL of other memory and were in essence, the personification of all of human history. Anyone crazy enough to adapt all those books shouldn't worry about confusing the audience. That's a given! Seriously though, making the the identity of the narrator and their relation to the events part of the ongoing intrigue, can be a good way to draw an audience in if done right. Of course done badly it can totally break the pacing an immersion and totally wreck the narrative. Like most things, it's all in the execution. Plus daisy chaining them like that is a good way to maintain a continuity of storytelling, especially when decades or millennia can pass between movies. For example, if you start GEoD with someone from the post-scattering period talk about Leto II in relation to the time they're now in, it gives the audience a slightly gentler lead-in to the subsequent story before the current one has even began. In short, it lends a larger sense of context and avoids the plodding, almost aimless "and then this happened" type of linear story telling. I'm pretty sure I read some where they'd already stared work on Dune 2 & 3 when the film hit theatres. Not sure if that was just early drafts of the scripts or actual pre-production. Also not sure if "Dune 2 & 3" would have been Messiah & Children or if they would have chosen to roll those two together and make God Emperor the third film. I suspect the latter because honestly, knowing Lynch I think he would have been *dying* to get to the giant man-worm film.