Moderators should be allowed to create and manage subcategories in their assigned category. It's a feature which is very needed.
I agree it would be a great feature. When you have unit or project oriented community, such as in big company, or in non-profit organization, it is very useful, and allow the admin to do more important tasks.
It is a good idea, I like it. Maybe a Sub-Mod plugin is needed?
totally agree with this
There is this plugin: https://github.com/yariplus/nodebb-plugin-modmin
Basically does what you want, allowing you to give someone a permission to manage a specific category - including creating subcategories there.