It was my understanding that Main is intended for polished final products, and that drafts, polls, and, well, discussions, belong to Discussion.

That's a reasonable distinction. But imagine this: A post which is a central place for organizing working together. Such a post is a very valuable final product in instrumental rationality, but it will inherently have continuous activity and discussion.

This post is not fully polished yet, but it's the best one we have of the sort, and having it as a main post right now increases the chances of this becoming the polished gem we'd like it to be.

I agree with you that if this post "dies out" then it could be replaced by a better version.