How about this for a workaround?
- At the end of the semester, backup the course including all users
- Restore into the new course for next year and hide
- Unenroll all the students.
- You should be left with the Q&A forums plus your questions
- Now reveal the course and have the new batch of students enrolled (as if by magic
A bit of a palava but I doubt whether this feature will ever get added to the current Forum since there should be a completely new Forum activity by Moodle 2.8 if we're lucky. Make sure to ask for it there.
Cheers
Mark