A "repeat task from completion date" feature.
The task will be moved forward from the current date. For example, suppose you have a task that repeats weekly and is overdue by 6 days. When you complete this task, it will be moved forward from today and the new due date will be in 7 days.
Great Idea. Like mowing the lawn or getting a haircut. It doesn't make sense any other way than this, because if it's overdue and you complete it then the next occurrence is early and will just have to be overdue again.
This actually exists. Use "after" rather than "every" in the due date field! E.g. "after ev day"