I noticed you pruned kdeplasma-addons as well. Figured I'd list the other repos/widgets that still have these keys:

Discover's update notifier widget

• https://github.com/KDE/discover/blob/master/notifier/plasmoid/metadata.desktop#L102-L103

Also Mycroft has a X-Plasma-RemoteLocation

• https://github.com/KDE/plasma-mycroft/blob/master/plasmoid/metadata.desktop#L45

In R242:bb0185ab1c3cdfd63e1471ce684a8c8ffd4c17bb#3641189, @Zren wrote:

I noticed you pruned kdeplasma-addons as well. Figured I'd list the other repos/widgets that still have these keys:

Discover's update notifier widget

• https://github.com/KDE/discover/blob/master/notifier/plasmoid/metadata.desktop#L102-L103
  
  Also Mycroft has a X-Plasma-RemoteLocation
• https://github.com/KDE/plasma-mycroft/blob/master/plasmoid/metadata.desktop#L45

Thanks for the pointers. Though I do not have working builds of those repos or are in contact with the developers, so will not touch them. If you do, please consider taking over the pruning there.
By what lxr.kde.org managed to list me, there are also some further repos where such pruning might be good. Sadly do not have the resources to go over all repos myself.