Hide-until (release time) for todos?

[Robert Goldman <rpgoldman@sift.info>]

Has anyone implemented a property that's the opposite of deadline for
Org TODOs?

What I'd like is a property I could put on a TODO that would hide it
from agenda display (probably with some preference that would permit
unfiltered display) until a specified date.

This would keep me from being overwhelmed by tasks that I have deferred.

Another possibility, I suppose, would be to have a special DEFERRED TODO
keyword, and just hide all the deferred tasks.  But then I would like
some processing that would automagically un-defer them later.

On the one hand, having TODO items change their status without human
intervention doesn't seem to be in the spirit of Org.  On the other
hand, it seems a bit odd to have a task that is TODO, but hidden --- it
seems like the TODO keyword should parallel the state.

As the tone of this email may suggest, I'm thinking about trying to
implement such a facility, so my questions really are:

1.  Does this exist already?  ISTR someone asking for this earlier, but
I didn't see a positive response to that earlier request.

2.  If the answer is "no," I'd welcome any suggestions for how to
implement this.  For setting, looks like cloning org-deadline and
tweaking org-add-planning-info would be relatively straightforward; then
I'd need to look into modifying the agenda commands.

Best,
r