Plasma Workspaces have been refined considerably. Work continues on updating widgets with new ones built with Qt Quick. This effort brings improvements in consistency, layout behavior, stability, ease of use and performance. It is also now easier to build widgets, entirely new Plasma Workspace layouts and other custom enhancements. A new QML-based screen locker makes Workspaces more secure.
List of features supported by QML but unsupported by Widgets will grow which will cause devs to rewrite apps using QML.
When all big apps will be rewritten, Digia will drop Widgets to save manpower needed for maintenance.