WordPress multisite introduces a new database table wp_blogmeta to store metadata associated with sites. This allows for the storage of arbitrary site data relevant in a multisite/network context.
It provides an alternative to using options and can be retrieved from multiple sites in a more performant way—without calling switch_to_blog(). Sites can now also be queried by their meta with parameters supported by WP_Meta_Query.
Note: A network update is required to install the new database table.
All of these functions are ONLY available in multisite, however they work similarly to other metadata wrapper functions, such as for posts, terms, comments and users. In addition to these functions, it is now possible to use the common meta query arguments when querying sites with WP_Site_Query or its wrapper get_sites().
Provided filter wp_update_php_url for a more dynamic approach on the code level. Replacing the URL should happen in cases where a more specific guide to update PHP on the given environment exists. E.g. screenshot:
Fatal Error Protection with the so-called WSOD protection (white-screen-of-death protection), A mechanism has been implemented to detect fatal errors and, in certain designated areas of WordPress, recover from them. E.g. Screenshot.
Note that, while the primary reason for implementing the fatal error protection mechanism was making the process of updating PHP less “dangerous”, it is technically not tied to the update at all. In fact, it will be enabled permanently and discover fatal errors under any circumstances.
The functionality can also be disabled entirely if that is preferred, via a new constant WP_DISABLE_FATAL_ERROR_HANDLER or, more dynamically, a corresponding wp_fatal_error_handler_enabled filter.
WordPress 5.1 will display a warning for those plugins that require a higher PHP version than the one currently active.