good idea, would make for some dynamic tasks.
But wouldn't it support procrastination?

The case for this would be for repeating tasks (but really any tasks that are well out in the future you dont want to forget about but not have at the top of your list today). Today a repeating task is always in your list according to however you ranked it. Say for a monthly task, once completed, the next one should be on the bottom at first then gradually climb the list as time passes until its due or over due.
Per fhettenbachs question above regarding procrastination, I dont know. I dont think it would support it. In the end if you are focused on the highest priority in order of due date, all should be good.

This is a duplicate of https://www.rememberthemilk.com/forums/ideas/2462/