Check out how Zulip does threads, it looks very similar to this. The main view shows a chronological list of posts along with its thread title, and you can clic

Check out how Zulip does threads, it looks very similar to this. The main view shows a chronological list of posts along with its thread title, and you can click on one to show the entire thread as a normal chat. Even PMs show up in the feed interleaved with everything else.