After many months of work and debate, Drupal 8 lands APCu (APC user cache) support in core for PHP 5.5 and up! The original issue can be found at the Drupal.org website - Built-in APCu support in core (PHP 5.5 only).
APC is a caching mechanism widely used with PHP, and APCu is a part of the APC caching mechanism, that caches data - such as variables. This will lighten load on database layer for PHP 5.5 and up. The reason why PHP 5.5 and up will be serviced is because starting with version 5.5, APC is included in the core of PHP. This will increase speed with which data is retrieved and served by Drupal.