I am wondering if there is a way to have a thread that is readable by anyone, but where the originator OWNS the thread and can selectively lock the thread, so only he, or those he has given permission to, can add posts (use buddy list?).
Something like giving moderator powers for a particular thread to the initiator of the thread. This could be one way to help keep threads on topic, and they could also be edited and cleaned up much later, maybe after a lively discussion.

Some of my favorite threads are the DIY construction projects. And some times I can't resist adding my 2 cents worth, or just gushing about how nice the final product is. But once a project has run it's course it might benefit from the same sort of editing as the Quick and Dirty 4430 thread.