Right, but they'll only do that if they're aware of such a system and it
is significant enough to make a dent in them. Further, it would be a
mistake to assume that *just* changing ASN's would be sufficient. The
act of changing ASN's could act as a trigger to re-whois ARIN for an
update of ownership, for example. The fact is that the information to
trigger a re-query of ownership upon a redelegation sort-of already
exists, though it is clearly imperfect.
My point was that if it was actually useful to "notice" when an IP
delegation moved, someone would already have made up a system to do this
So my best guess is that there isn't a really strong incentive to pursue
some sort of notification system, because you could pretty much do it
as it stands.