Have an optional button that can be selected to set the due dates to hard or soft. Where a hard due date is an actual due date and there are consequences for missing that date and a soft due date is more for managing task scheduling.
I like scheduling tasks and giving soft due dates to all of my tasks. Some of these are just to ensure that I look at the task every week, month, quarter etc. Having hard due dates would be great as it would prevent rescheduling task with really important due dates.