Currently, when you double click a picture in the "Thumbnails" view in order to open it in the "preview" view, it can take a few seconds until it is displayed, with nothing seemingly happening during that time. This is specially relevant for pictures which are several MB in size stored in a NAS. A simple loading or progress indicator would suffice to provide some feedback that the picture is currently being loaded.
I know this is an old suggestion, but have you given any thought at this? I am currently using digikam with a library that is behind a relatively slow network. Some pictures take 5-10 seconds to load, depending on the size. When I double click on a picture, I have no feedback that it is being loaded, until a few second later when the picture suddenly appears. Sometimes it feels non-responsible and it makes me double-click again, just in case. Maybe the progress bar could be used as an indicator that something is being done?
On the status bar, Image Editor uses a widget on the left side to show file name or display a progress bar while loading/saving. The same widget can be used in preview mode. Gilles Caulier