SUMMARY
Time and again I browse through a hierarchy of folders, most often to view photo albums. That means I either have to click through a tree view in a sidebar with the mouse, or when I only use the keyboard, go one folder level up, select the next one and press enter (in Gwenview) or – in Dolphin’s detailed view – press left to select the folder, left again to close it, go down to the next folder and right to open it. Due to https://bugs.kde.org/show_bug.cgi?id=426716, being on a Touchpad is not very practical and on a touch screen the user cannot scroll on a breadcrumb item at all.

We already have a “Go up” action. So I propose two new related actions: go to previous sibling folder and go to next sibling folder. The Icon could be double-arrow left/right (i.e. the skip symbols from a media player), and the default keyboard shortcut something like Ctrl+Alt+Left/Right (unfortunately, Alt+Left/Right, which would better fit together with Alt+Up for “Go to parent”, is already taken). I got this idea yesterday when I was using Ranger, the vim-like terminal file manager, which provides [ and ] to do what I just described.