This would be useful, but no plans for it at the moment. The primary issue is that nesting would complicate the sharing model and how folder settings are applied
For example, if you had folder "ABC" that was shared with a@example.com and b@example.com, and it contained folder "XYZ" that was shared with "c@example.com", what would you expect the permissions to be for snippets in folder XYZ?
Just c@example.com? Or should it be all three users? Or maybe just the permissions of the top level folder and any sub-folder permissions are ignored?
Reasoning about hierarchical permissions like this is quite confusing and there is no default mental model people have for it.