I'm curious if this is popular enough to continue beyond the first book, if they're going to split any of the others.
I really think you can get through the others well enough one film apiece. Although GEOD will need a lot of changes... Honestly, I'd skip it if I was making the movies. It's not needed for the last two which are sexy action adventures in space and could sink the whole franchise when you have three hours of various people getting lessons in philosophy from a giant CGI worm.
They obviously have faith in Dune that they're already working on the TV show but, at the same time, not enough faith to have filmed both movies back to back. I really don't see this bombing like Lynch's version but it could hit the Blade Runner/Mad Max spot where it is critically acclaimed but financially "Meh". Then they will probably be waiting for the shows success/failure to decide whether the IP is worth continuing to adapt or not.