How to define positive AND negative depth on taxonomy filter in views' module?
I've done stuff like this (eg, World and nesting of regions in the world with heirarchical taxonomies).

Take a look at Taxonomy Edge. It provides view integrations to provide search filters for "Taxonomy edge: Parent term ID" and I believe "Taxonomy edge: Parent term has child term". I mean it adds some useful parent and child Views search filters (I dont believe it adds a single positive or negative search as you've described).