Deferrable check constraints

I recently wished for deferrable check constraints while doing some
crash-recovery stress testing.

I don't know how important they would be for real-world cases, but the
SQL standard does seem to require them, so I think they would be
desirable just for that reason.

There isn't an entry for this on the wiki TODO list. I wanted to add
an entry, but I can't find any mail threads to link to about why this
isn't wanted, isn't possible, or isn't easy. Or for that matter, *is*
easy, but no one has gotten around to it.

Is there some canonical discussion on this topic that I'm not aware
of? (The mail archive search interface is not so helpful with common
words like "check".)

Cheers,

Jeff