When using sub-tasks, "task creep" will likely occur and original task due date may get overrun. Since the task is effectively being dictated by the sub-tasks, it would be great if the task due date was automatically updated to equal the latest sub-task due date. Fundamentally, there is no reason a task should ever be due before its own sub-tasks. This would be checked and calculated on any sub-task due date creation or change.
This could / should be applicable to the due date of project (when/if) vs its lists, a list vs its tasks, and maybe project vs its tasks. Unlike task vs sub-tasks, the project and list objects should have a switch to select for "auto-update due date".