In reply to Nick.

Hey Nick! I did a little research on the four items you mentioned in your comment. I like to speak with as much accuracy as I can!

You had five different things, I think:
- Meta boxes not showing (in WP5.0-beta1 + GB4.1)
- Can't disable Gutenberg with a filter (in WP5.0-beta1 + GB4.1)
- Width of the editor is not resizable (in WP5.0-beta1 + GB4.1)
- Issues with ACF, but it sounded like you thought they would be resolved
- Classic Editor Block does not display custom buttons in the toolbar placed by themes and plugins (in WP5.0-beta1 + GB4.1)

Fortunately, the Gutenberg team is aware of most of these and fixes are in progress (meta boxes https://core.trac.wordpress.org/ticket/45172, improvements to managing the width of the editor https://github.com/WordPress/gutenberg/pull/10956, custom buttons has a patch in the works right now).

Disabling Gutenberg with a filter is not possible with 5.0, but you can with the Classic Editor plugin. Some of the people who want to learn about the new editing experience at their own pace won't be familiar with code. We are trying to remain aware of the many people who won't know how to work with filters.