As I understand it, the meta-thread is for meta-level discussion of the site in general: new feature ideas, what norms to encourage, how we can be more welcoming etc. I think you're the first person to suggest moving all meta-level excursions to the meta-thread. This is an interesting proposal (you can discuss it on the meta-thread!) but it isn't yet what users are expected to do. We have meta-level discussions all the time in the comments to top-level posts when the meta discussion deals in particular with our discussion of that top-level post. Sometimes those discussions involve principles than could apply to a broader range of discussions but that doesn't mean we need to move the conversation.