I only see one problem with this. If the thread was on the list of threads then people would enter the forum, look for the rare and exit before using up a turn rather than pwning the forum. The rare thread would have to pop after you take down at least one thread and would then also need to be locked in for that forum otherwise the speed runners would constantly miss the rare threads.

Otherwise this is an excellent idea and would add a lot to replayability for vets between episodes.