The system settings need a ton of improvements and some reorganization.
For me personally this has a high priority.
The are so many inconsistencies and issues.
Currently there is a mixture of styles, behaviours and frameworks used for KCMs and they can be very confusing, which is a big problem.
We should port the system settings and every KCM to Kirigami/QML.
We should start by porting every KCM to Kirigami/QML (#plasma_kcm_redesign).
After that we can make further inprovements to the KCMs and reorganize them.
At the end we can port the two system settings hubs/start screens/layouts that are used now to QML/Kirigami: Icon View and Sidebar View (drop the old and ugly tree view).