Plugins are implemented in (at least):

• ffmpegthumbs
• kdegraphics
• kio-extras
• marble
• mobipocket
• plasma5-desktop

KIO itself only uses the service metadata, i.e. the ThumbCreator service type and properties like CacheThumbnail.

The plugins are instanced from the thumbnail KIO worker in kio-extras. While currently only the plugin entry point is used (via QLibrary::load/QLibrary::resolve), there is also a need for the metadata - the directory thumbnailer should respect IgnoreMaximumSize, CacheThumbnail, ..., and should set the Software PNG metadata field based on ThumbnailerVersion.