Version: (using Devel) ability to turn the nav.panel off directly As in Dolphin and my other apps -- it feels natural to close the pane by clicking on close (x) widget.
They are not the same thing: Dolphin widgets are dockable panels, that can be moved and detached from the main window. Okular's navigation panel is a part of the main window.
Ok, but still it would be useful to close it directly, move it to the right.
So clicking on the icon of the active pane and Settings -> Show navigation panel are not enough for you?
Yes, the object should be self maintained -- as toolbar for example or window. Besides, I as user see it again and again, and when I run okular there is feeling "something missing". Not a big issue of course, but it would be nice to have consistent UI (among KDE).
Won't happen