The forum garnered quite a bit of feedback from the community. In a few words:
If we make it, it would be better as a user centered feature (vs admin controlled)
The actual use case is too niche and unclear.
Given this was first proposed in 2015 (https://design.xwiki.org/xwiki/bin/view/Proposal/NestedDrawer#History), and the discussion on this improvement has grown stale since then, I'll just close the improvement as "Won't Fix". Feel free to open it back with a comment explaining your use case if you think this should still be tackled.
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