In reply to Stephen Vaughan.

Current phase of Gutenberg - the "editor" - is only the beginning. The later phases of Gutenberg will replace everything in WordPress backend, like widgets, menus, media library, user management, everything. Currently existing custom fields plugins like acf, pods, toolset etc. will become completely obsolete, same for all the current pagebuilders.

Consider Gutenberg editor as some sort of a trojan horse. The "all is fine" Classic Editor plugin should/will convince many to upgrade to 5.0 "without risks".

Once people have upgraded to 5.0 and start using Gutenberg editor, they can not go back to 4.x and also can not simply migrate to other CMS because Gutenberg editor puts all its blocks-markup and parameters etc. as one big "datablob" right in the post_content field.

Then the other phases of Gutenberg will be announced and merged to core, users are more or less locked in, a new infrastructure with pay-per-blocks will replace most existing themes and plugins and Gutenberg project will look like an huge success (at least in terms of number of websites).

The trick with Classic Editor is, now it's a filter, later various functionality including classic editor itself will be moved from core to the plugin, so this functionality will be simply gone as soon as Classic Editor expires, which now has been announced clearly for 31.12.2021.

The four phases of Gutenberg project, the moving of core code to Classic Editor plugin, the "you can always use Classic Editor for now" talk, all that has been communicated several times at support forums, github issues, slack, twitter and make.wordpress.org/core/ so everybody can read and draw own conclusions.