If I have many filters on a structure board it would be nice if I could group them into a hierarchies at least 2 levels deep. This allows for more filters and less screen space consumed by the filter panel.

For example (1 filter vs. 6 filters on the panel)
Panel Filter -> Assignees
Dropdown L2 -> Team a
Dropdown L3 -> User 1
Dropdown L3 -> User 2
Dropdown L2 -> Team b
Dropdown L3 -> User 3
Dropdown L3 -> User 4
Filter Box L2 -> Team c
Dropdown L3 -> User 5
Dropdown L3 -> User 6