I really like the idea and general form and the use of an interactive mockup to gather feedback, so this is just minor impressions and comments. Because it's such a high-fidelity mockup, I assume you are looking for visual design feedback as well as functionality. Feel free to ignore that half if not.
Random feedback not intended to be in order of importance or imply that it is important or expects a response.
The body text seems large compared to Wikipedia page content normally. That's a good thing. The rest of the web has headed in that direction, but it would look more integrated if other parts of the site got less cluttered and more readable to match.
It's not clear to me why there are so many different font sizes for elements on the page. A single comment has about 8?
Is mark abusive more important than other tagging or actions that it needs to be brought out into the box?
Is mark abusive the only action that applies to a single comment rather than a thread? I suspect I want to be able to tag individual comments and close and oversight should probably comment based too.
I'd like less clutter. Author meta data, mark abusive could hide. Borders and header boxes could be more subtle (or go)
I _really_ like the highlight unread and auto mark as read but the current experimental implementation is not quite right for me. The contrast between unread and read is very high, so when it suddenly changes it's a bit alarming. I think it also changes too early. It changes as I start to read that box and I distracts me or beats me to even starting. I think my habit is to scroll what I intend to read next to near the top of the screen so for me the change would be more natural if it faded out a second or two after that box started to scroll off the top of the screen, or on reload for pages too small to scroll. At the moment it looks to be tied to entry at the bottom or rendering and gets marked before I have read it.
I know it's common, but I don't like multiple search boxes on one page. If there's not a clean way to use the top level box for both sitewide search and in page search on pages that support it, then I think they should at least look the same and have the same action button.
I can't see in the test data how it handles very deeply nested reply indenting?
I assume the final version would resize to fit a range of page widths?
The same pieces of content seem to be being called Messages, Replies and Responses in different parts of the screen. Or maybe Replies and Responses are synonyms and Message and Topic are synonyms.
Why does New message get a plus sign but Reply get's neither a new nor a plus?
Replacing the term "talk page" seems unnecessary. The same purpose with a new UI could reuse the old name.
I like that it reuses the same style as for unread indicator and Echo Notifications.
I'd like a way to navigate from the top of the screen to the newest reply. It looks like it's ordered by most recently updated thread, not by thread start, so in line with my request for less clutter maybe each "last updated" timestamp could send you to the comment that refers to.
Keep up the awesome work. I hope you get lots of good feedback, ignore 3/4 of it and come up with a great model
Luke Welling