I often use Q&A-forums with a single question in my language classes. The advantage over "assigments" is that the pupils can compare their answers once they have posted and even add comments, but they cannot copy from each other.
Then I need to set the forum to "read only" at a certain date. I usually do this by withdrawing the permission "Reply to posts" in the forum from the student role.
It would indeed be nice to be able to close or reopen a forum or even a thread with a single click..
Adding a closing date in the forum or thread settings would make it even more comfortable.