As discussed on T8126 & irc, as simple approach to have a clean list of Plasma 5 compatible Plasma Themes, a separate Plasma 5 Themes category will be introduced at time of Plasma 5.16.
- improve theme documentation, like theme porting (https://techbase.kde.org/Development/Tutorials/Plasma5/ThemePortingToPlasma5)
- announce plans with the new category to theme creators, e.g. 3 weeks before switching:
- create & switch to new category:
- create new category "Plasma 5 Theme" on store.kde.org (some days before 5.16.0 tar creation (Thu 2019-06-06)
- add news to store.kde.org/opendesktop.org about new category
- change in plasma-desktop's plasma-themes.knsrc the entry to Categories=Plasma 5 Theme after that & before 5.16.0 tar creation -> D20898
- backport the plasma-themes.knsrc to Plasma LTS versions, ask distributions to add a patch until the next LTS release
- automatically move or ask theme creators to move their respective themes to the new category (latter better as it will show which themes are maintained)
- add related notes about theme fixing and the new category to Plasma 5.16 release notes
- add unit test for KNewStuff to ensure content with old categories in the knsregistry is not ignored by design and not just accidentally :)
- in the sidebar of store.kde.org move the old "Plasma Theme" to some subcategory, so it's not confusing (no own proposal, the current list gives me no idea for some pattern), after half a year or so, when most themes have been moved