You can already do this, @Natalie_Michel, at least in a couple of ways, so maybe this will help:
If you’re looking at subtasks in the right-side task detail pane, you can multi-select them (click the first and shift-click the last) then from the “. . .” menu choose Delete selected subtasks:
Sometimes you may want to gather subtasks in an advanced search for multi-selecting them there.
Thanks,
Larry