Gutenberg to Offer New Approach to TinyMCE in WordPress 5.0, a Plugin to Bring Back Old Interface Will be Availablewptavern.com | Sep. 12, 2017 | 8 min read
This post confirms that there will be a plugin available to disable the new Gutenberg editor. It also seems there will be a plugin to get metaboxes working. Wasn't the plan to have metaboxes working out of the box?!