Sorry for reviving an old thread, but I'm new to Joplin and this is a big issue for me. So far I love what Joplin can do, I just hate the notebook / notes layout. This is one-too-many panes and it breaks up the logical act of browsing for a note. If I'm browsing the notebook tree, the contents of each notebook is critical! I shouldn't have to click inside each one to view the list of notes in it - this is not intuitive! Showing the contents in another pane drags my focus away from the tree and also force-updates the editor/preview panes to one of the notes in the notebook, or blank, if there are none. It's not good UX, in my opinion.
@sebastienPoussard @athalef did this ever get resolved? Was an github issue ever created (I can't find one, and none was ever linked here)
Edit: This is a duplicate request: Notes in tree structure
Edit 2: So it appears that the policy on feature requests is, post on Discourse! Perhaps that's why there's no github issue.