The conservative choice of PHP 5.2 as the minimum requirement for WordPress doesn't stop performance sensitive sites using later versions of PHP, or HHVM, or Ph

The conservative choice of PHP 5.2 as the minimum requirement for WordPress doesn't stop performance sensitive sites using later versions of PHP, or HHVM, or Phalanger, or whatever floats their boat. Indeed, only 30% of WordPress installs use PHP 5.2. Runtime features are not a problem for WordPress users. If you think the minimum requirement is limiting potential for optimisation, what are some relevant language and library features in subsequent versions that the WordPress team can’t use?