Such discussions should really be in this forum:
I reckon the idea is that comments should not be used for big code snippets. But sometimes there's no other way. The comment system in the QA forum is a very poor forum implementation. It would be better to have the full forum (that's available for articles and message boards) attached to a QA thread. That way, any meta discussions take place in the forum, while only valid answers are posted in the non-forum QA portion of the thread.
Comments can also exist but merely for very simple queries to and fro, so comments should probably be limited to 20 words or so (256 characters).