I don't think the proposal is a good idea: it adds a trivial inconvenience to posting, and adds more noise to discussion making it harder to find the latest actually open thread. I predict the result would be at least one of: people post in the wrong section, people ignore a number of the categories, or people post less overall.

I'm in favour of more frequent open thread posts, but I think they should remain a single open thread. (Actually if I were making changes I'd probably fold the media recommendation posts into the open threads).