Hierarchical Select with taxonomy in Views
You can achieve this by combining Simple Hierarchal Select and Views Dependent Filters. So you use SHS for selecting the taxonomy term, and then set a dependency that if a term is selected on the first taxonomy, show the second taxonomy.


Add your first/primary taxonomy that you will be using to determine the secondary options. Don't select any terms, expose filter.
Add your secondary taxonomy, expose filter.
Add a Global: Dependent Filter to your list of filters.
Your Controller Filter is the first taxonomy that will be deciding which second field/taxonomy will showing up.
The Controller Values are the values from the taxonomy selected for the Controller Filter. Pick the term which when selected will show the dependent taxonomy. The dependent filter is the secondary taxonomy that you want to show up.


There does need to be some specific ordering going on, like the dependent taxonomy needs to be above the Dependent Filter, but I can't remember exactly. I'm sure you can figure it out from there.