Foren / Cotonti / Skins / Bootstrap admin theme

Both of the included plugins are optional. If you don't install them you don't lose any truly important features, just usability. Configsiblings is indeed extremely simple to include in admin.config.php by default. It provides a trivial feature and it makes sense to make it part of the core package. The other plugin, 'admintheme' is nice as a plugin because that allows you to disable it (in part or fully), causing the default templates for page and user listing and editing instead of the bootstrap enhanced ones.