That UI does look great.

I too really like the cats/tags at the bottom of the editor, but I wonder what happens when a couple custom taxonomies get added? A few metaboxes? Edit Flow? etc...

I'm not a fan at all of the giant post format icons. Too much space for a one time selection. Those should be in a drop down just like categories.

While I applaud all efforts to imporve the Post Editor UI I think it needs a mobile first design that includes all the complexity of a CMS or multi-author magazine. Can the UI handle metaboxes/cusom fields, multiple taxnomies, post format changes. Make all that work on mobile and then stretch it out and strip it down to what it'd look like on a site that is "just a s single author blog".