Hide subtasks on the calendar task pane.
The calendar task pane is low on space. It would make sense if there was an option to hide child tasks and only show top parent tasks. It would work nicely on the calendar. Seeing the parent task on the calendar jogs your memory of the subtasks that need to get done. And when the parent task gets completed all child tasks get completed as well. I visualize this as an option right on the top of the calendar task pane above the "Task Score, Most Recent, Whatever" selection.
Alternatively, this might also be accomplished by allowing the user to toggle this on and off within the individual tasks with another "!" action. "Hide from Calendar View". This might give the user a bit more control as well. As they are planning a project they can toggle on and off which parent tasks they want to see. Although this may get confused with the more general "hide" action.