Showing replies "in-place" like Reddit, instead of show 'em at the bottom

Maybe you are interested in Web Discussions: Flat by Design

But you can still expand direct replies to a post at its bottom. So below your post, you see an indicator about my reply, and you can read it right there, even if there would be other posts in between. By default, some of these indicators are suppressed, but you can adjust the settings to fit your needs.

You should also take a look at Discourse Post Voting