"post x/y" tells you how far you are in the page, but only if you think about it. There's no longer any intuitive connection between the scroll bar and page position. The End key stops working intuitively, sends you to the end of currently loaded posts and then loads more posts so 1 second after pressing it you're not at the end of anything. Then there's the lag as you hit the top or bottom of currently loaded posts; even if you don't want to read any more, you get more. That's clever if you're a tabloid magazine because it entices the reader to read more, but the impression I get is it's not productive.

For maximum usability, why shouldn't the app support both infinite scroll and paginated, and let the USER choose (by url slug or GET param)? (Or by user setting if logged in)