Just FYI, unless I am not understanding you correctly, that it really different from how defer dates are intended to be used. The idea of a defer date (known as a “start date” in OmniFocus 1) is to tell the system that you do not want to work on that action until that date. A task with a defer date in the future will be “Unavailable” until that date. Once you hit that date, the task will become “Available” (and will then show up in any perspectives that you have filtered to show only available, as opposed to remaining, actions).
I can understand why you would be tempted to use defer dates as “soft” due dates, but I think you might run into a lot of problems with this approach. To see those dates in any custom perspectives, you’ll need to show all “Remaining” tasks, instead of just the “Available” tasks. But that means you will also see other “Unavailable” tasks, like tasks in a sequential project that depend on some other task. Things could get confusing really fast.
You might want to check out this discussion on using defer dates:
