bbPress.org

Should not be too hard to implement into /bbp-api/topics/id (https://github.com/ePascalC/bbp-API/wiki/API-routes)

You get the topic data there and then an extra array with all replies.

Along those same lines, an object including the authorId, author name, and author hashtag in the api would eliminate a need for another custom api call for user info. WP does not allow hitting user info publicly to prevent name scraping I guess.