Categories as filters
One feature I really like about Vanilla 2 is that with the category list on the same page as the discussions list, categories work as filters.
However, the effect breaks if you make sub-categories, because I would expect that when I click on a root category that it also lists the contents of its sub-categories, whereas it doesn't.
In the dashboard there's the option "Display root categories as headings.", I wonder if it would be a cool feature to add "Root categories include sub-categories" (with better wording), unless this is already a feature and I missed it?