Good point on the content-segment tags, since all outer tags are indexed, and these don't seem like they need to be. Probably have to rethink this part. I haven't really gotten to the higher layer stuff like that yet, beyond the rough first draft. I was imaginging application-layer tags (longer ones) inside of the content for stuff like this, but it's not written that way.
Discussion
You'll also want to find a way to avoid duplicating tags if they need to be indexed but also used in content. Which means content likely needs to be able to reference tags in either place.