I think that I once saw somebody, elsewhere, suggest that it would be nice to have a bulk task closure feature available within the Matters view. Maybe I just imagined that, myself.
I like the idea, though I can picture the GUI starting to get crowded with quite a few buttons.
Perhaps one approach to providing that feature while minimizing clutter would be to have tick boxes in a narrow leftmost column in the list of tasks and have a section of buttons on the left related to manipulating tasks, but have those task manipulation buttons become visible only when one or more boxes is ticked and become invisible as soon as no box is ticked for any shown task.