This may seem like it’s out of place or just another UI convention that is going to muddy the waters but people should really follow the development of the Gutenberg project more closely. They’d see this isn’t random or out of place but instead it is laying foundations.

Something to note is this UI/UX comes directly from ongoing work being done to completely redesign the WooCommerce admin UI.

Read between the lines and this is where the UI/UX of the entire WordPress Dashboard itself is going.

That nav that slides in and out on the left? It’s going to replace the main WordPress Dashboard navigation eventually.