As discussed in https://bugs.kde.org/show_bug.cgi?id=422875#c3 this is a sub feature request for a "Wallpaper" KCM.
We've gotten this request a number of times before, yeah.
However we already seem to have a Phabricator task tracking this work. Tracking it in two places is redundant. Let's continue at https://phabricator.kde.org/T12622.
Alright