OK, I think I am starting to get a better sense of what you’re trying to do. I don’t immediately have great thoughts about how that might be done in practice, though. If you do end up with something closer to what you want using custom sections or additional customization on top of the sidebar, I’d love to see what you come up with.
I think this other topic about using tag groups may also be of interest to you: In the sidebar, can I list the tags by group?