Q&A Threads - one post per user, with comments

A lot of communities don't quite grasp the concept of Q&A threads/nodes and despite the best attempts at moderation, these threads frequently fall apart and become useless because users are used to posting conversationally like they do in normal threads. Q&A threads are (IMHO) clearly modeled after Stack Overflow and other such sites where the point is to ask a question and each user is afforded a single response, to be rated against other users responses. The best rated response becomes the highlighted response.

The problem, as I see it, is that in Xenforo's implementation users can post repeatedly just like they would in a normal forum thread. This leads to some replies that are low-quality answers or not even answers at all. Furthermore, the thread starter can also post responses in the thread which can further confuse things. The community doesn't downvote these responses, so they're never programmatically hidden.

I think that in Q&A forums/threads, each user (including the thread starter with their question) should be limited to a single post per thread. The comment system used in say, profile posts, should be implemented in these threads for follow up or side remarks by any user (again, modeling Stack Overflow). If this isn't going to be developed into the core product, is this a feasible add-on to build?