I dislike this for one main reason: Scrolling. HN as it stands now is nice and compact, easy to scan through stories without the need to scroll a page. This breaks that, which creates an obstacle that isn't necessary.

Also, when you select another page, like "new", then the active color of the navigation makes that link invisible.

Overall it just feels like adding white space for the sake of adding white space to try to achieve something that feels modern, but in reality inhibits useability.