Issue Overview

WP allows register meta fields in similar way as is for PostType or Taxonomy. Main difference is that it doesn't have as many as functions as MetaBox, but it is more or less standardized workflow to define post/term/etc fields.
Most MetaBox can be reinitialized with WP functions https://developer.wordpress.org/reference/functions/register_meta/ or shortcut functions for posts or terms https://developer.wordpress.org/reference/functions/register_post_meta/ https://developer.wordpress.org/reference/functions/register_post_meta/
With sanitizing, name + description (as description field), multiple (single as false) and clone (object or array type) support or clone_as_multiple (single false + object type).

Expected Behavior

Developer can use built-in functions as https://developer.wordpress.org/reference/functions/get_registered_meta_keys/ and all related functions.

Current Behavior

WP doesn't any clue except MetaBox about registered meta fields.

Possible Solution

As Extensions module to MetaBox, no needed in core.