The default wallpaper to use comes from plasma-framework [Wallpaper] defaultWallpaperTheme=Next defaultFileSuffix=.png defaultWidth=1920 defaultHeight=1080 due to the out-of-sync releasing it will never be possible to change the name, and most importantly the suffix. This is a problem as .jpeg would save /soo/ much disk space. 3.2Mb instead of 29Mb Can we just get rid of this suffix thing and look for all image file extensions?
that should be possible and should probably be done anyways however keep in mind, that for wallpapers that are drawings (like the default one) usually they have lines that are too sharp for jpeg to be acceptable so in order to use jpeg, either the wallpapers should be more blurry, not have any sharp edge, or move to using a photo by default
Moved the discussion to https://phabricator.kde.org/T12611.