Interesting idea. I like how it gives the user a three levels of nesting at once, though there is something to be said for readability if the screen has all three levels of hierarchy: Sidebar/Categories → Latest → Topic.
I think this would be quite cool to see as a theme/theme component. How would you keep the screen tidy and readable in this layout? I feel like the topic getting half of the screen, with the other half being sidebar and latest is a little bit too noisey. For example, hiding the sidebar in this view might be an option, though many users are not aware of this functionality and it would lose the benefit of access to the highest level of Topic hierarchy(Categories).