Hi Dave
I don't think it would be feasible to add this as a feature, I think it would need to be a whole new Task View.
I wouldn't want to add it to the Task View because that's always meant to show the actual task hierarchy.
Adding it to the List View would be possible, maybe as an extension to Multi-sort, but without being able to expand/collapse the groups.
Which leaves us with a new Task View.
BTW, what is that app in the screenshots?
Dan