Haha. The issue i see with sidebars, at least in this theme, is that youre all going for minimalism, which means chopping all redundancy of info out of each page. If you can see all recent replies on the category page, you dont need it on the thread page too.
I could be wrong though. Node does several things i never wouldve thought of doing, which is good. No forum puts the actual replies on the front page. And nobody decontextualizes those replies by not saying at least the name of the thread.
Its very different and im trying to figure out peoples reactions to it. It might be more natural, since people rarely care about what started a conversation, and only care about the last thing said.