Actually, watching your example I realize that the step when you select a file in the hierarchy, and “nothing” happens – e.g., no editor is opened on the right – won’t be possible in Fibery.
Unless I’m overlooking a use case, I think that as soon as you click/select an element in the sidebar, a pane is opened on the right.
I realize that I’d like to have the sidebar as much as possible always in sync with the current pane like in VSCode ↓
I said “as much as possible” because I’m conscious that it will only work for Documents, Pages, and Views. When clicking on an Entity link, there won’t be anything to reveal/select in the sidebar the Entity has no visual representation in it, just many views possibly listing it.
I’ll probably open another topic for the “Keep sidebar in sync with current pane” 
→ Keep sidebar in sync with current pane - Ideas & Features - Fibery Community