I think the automatically added version numbers WP adds to all stylesheet/script urls could be better.
At the moment the WP version is added if no version is specified by wp_enqueue_style. So now a browser will re-download the stylesheet if WP updates. But it's unnecessary. Also if a theme get's updated, the browser don't get to know it and uses the old css. This can lead to broken layouts.
I would like to see WP adding the version number of the theme to styles/scripts added by the theme. Styles/scripts added by plugins should get the version number of the plugin. Files added by core shold still use the core-version.
I use this code in my themes. Doing it automatically, would be more nice.
// Save same data about the theme into a variable
$child_my_theme_data = wp_get_theme();
// Enqueue a CSS style file
get_stylesheet_directory_uri() . '/style.css',