I think it would be great if we could mark topics as answered. There is a great site that does this here under the "Reputation" section: https://answers.laserfiche.com/home/tutorial/1#earn.
When someone asks a question and marks one of the replies "This answered my question." they receive reputation points. On nop it would translate to karma. Also, when someone answers a question they receive reputation points as well. It really helps drive community involvement. Another way questions can be answered is by a nop team member.
It would also help people know which forum topics still need a reply or have not been solved. Of course there is the chance the user doesn't mark an reply as an answer, but overall I believe it would be a great addition to the community.