This is an obvious benefit for developers. Maybe even for site owners, as they can get something out of these benefits too indirectly, but I think it's too abstract to include in the site owner benefits list.

Maybe the page could/should list some examples:
http://php.net/manual/de/class.messageformatter.php - could be useful for a better/faster way to translate things in WP
http://php.net/manual/de/normalizer.normalize.php - could be useful to fix encoding problems.
etc.

@Zodiac1978 That's a good idea, once we start working on a developer-related version. For now as primary goal however the version for site owners is most important, since they are the majority of WordPress users.