Important note: Closing this issue means we update the minimum WP supported version of the plugin to 5.0. (Edit: Done in #13370)

Now that WordPress 5.0 is ready to be released, we need to start working on the next phase and ensure we don't duplicate code in the plugin.

Things that should be removed from the plugin:

• REST API endpoints and tweaks (Framework: Remove 5.0-merged REST API integrations #13408)
• Block parsing, rendering utilities (Plugin: Remove 5.0-merged block registration functions, integrations #13412)
• php files adding the MetaBoxes support (Plugin: Deprecate metabox supports, fall back to core #13449)
• Miscellaneous core compatibility (lib/compat.php) (Plugin: Remove redundant core compatibility from plugin #13442)
• Bootstrapping the Gutenberg editor (already done in Core) (Plugin: Remove replace_editor filter, extend core editor #13569)

See Project: https://github.com/WordPress/gutenberg/projects/23

The php files that need to remain in the plugin are:

• Scripts registration (overriding)
• Dynamic blocks registration