Cool idea! To take the provided example, with nested tags you might create #religion/belief. But also you might want #belief and/or perhaps, within another context #emotions/belief.
I think there is definitely something to be said for a feature that would automatically return all notes tagged with the word belief occurring at any level in the nested tag structure. This can be accomplished using regex searches with Obsidian native search or Dataview queries (see links below). That being said, if there were something like a “wildcard” mode for the Tags core plugin, that automatically did this, it would make life a lot easier and nested tags more flexible.
Related: Dataview regex query to match all occurrences of a subtag
Also related: Searching for sub-tag
Thanks!