Well, i was going to include it in final v1.4 version anyway, but it might take some time to finish. Most wanted thing for now is proper FileChooserUI implementation and some critical fixes for menus and UIs. After finishing those i am going straight to dockable frames
But there is also a chance that this component will be needed in our upcoming project and might come out sooner than other changes. In that case dockable pane "sketches" might appear in preview builds in next few weeks.
To summ up - i'd say it will be available in a month. Still, everything depends on the free time i will have to spend on WebLaF project and tasks i will have to complete.