follow-up to #1872522: Compiled data in PHP storage is cleared too late in drupal_flush_all_caches() for the recover script that got pull out form the patch.
In Drupla 6, update.php would serve as a recovery script (cache clear and rebuild module list). We lost this in Drupal 7, and it's never been replaced in core.
For Drupal 8 especially with the dependence on config and compiled PHP on disk we need to have such a script easily available.