It would be great if we could set different transparency level for each panel/dock on desktop, which it seems is controlled mostly by an image (e.g. panel-background.svg) in the plasma theme, applied to all panels. This feature will enable a desktop configuration, for example, consisting of a top panel with some or no transparency, a side panel with some transparency, and a dock with full transparency.
Whether or not a panel is transparent or not is already per-panel, so this is really just asking for granular transparency settings, which makes this a duplicate of Bug 457215. *** This bug has been marked as a duplicate of bug 457215 ***