[css3-animations] [css-transitions] animation-delay animatable?

Would it be possible to extend the Animation draft to allow animation-delay
to be animatable?

The motivation here is that there are cases where it would be useful where
transition behaviors are desireable, but the changes desired are only
provided by animations. For instance, using :hover in a navigation menu to
disclose sub-items. If an animation is used for the disclosure, when :hover
is removed, the items simply vanish; if the no-hover style includes the
animation, that animation occurs on page load.

If, instead, there were a paused animation attached to the element, and
:hover could transition animation-delay back to -duration, then the
animation could play out from there, and reverse when :hover was removed.

There's the obvious objection that the behavior of animating
animation-delay from within an animation would be badly defined; perhaps
that's simply defined to have no effect?

Is this possible? A bad idea? Unneeded? (although I've yet to see a way to
accomplish this effect without this CSS behavior.)

Judson