Thanks for the confirmation. Yes, you could collapse the parent tags in the sidebar, but there are hundreds of those for me, so it's still pretty unwieldy. Also, since you can nest tags in a deep hierarchy if you want, unlike the 2 level notebook-stack system, it would be even better if you could continue to drill down.
Would love to see nested tags we can intentionally drag into the sidebar, like stacked notebooks, and be able to expand/collapse them as needed.