Birgit Pauli-Haack reports in the latest issue of the Gutenberg Times that the first version of inline commenting is coming to WordPress. This is part of the Collaborative Editing phase of Gutenberg. The article reports that Pooja Bhimani of Mulidots and other core contributors have released an experimental version of inline commenting for the block editor. Currently you will need to use the Gutenberg plugin version to test it and also enable the Block Comments experiment.
With the experiment enabled you will see a new menu item on the three dot menu on the contextual block toolbar. There is then an item to open a text input in the sidebar to add your comment. A new icon appears in the toolbar of the block when a comment has been added. Those with editing permissions can then edit, delete, reply to the comment, or resolve it. When you click on the canvas, you can view all the comments for that particular post. Using the star on top of the comment sidebar, you can pin the icon to the top of the screen for easy access. You can use comments on pages or posts or any other Custom Post Type. However, once the post is published, inline comments are disabled.
The experiment is still in the testing phase and you can track its progress using this GitHub tracking issue. It will be included in the forthcoming Gutenberg 19.6.
