well, imiho, you were already three klud^H^H^Hheuristics deep
Heh! I have to admit that it has its problems, but it seems like not
a completely rotten idea. In order for it to work nicely, you
probably need an extra protocol, so that the DNS server doesn't have to
be responsible for all the validation and bookkeeping, and so that you
can have, *ahem*, leases on the PTR records, so that they get cleaned
up when the registrant goes away. I think we've pretty soundly
rejected the idea that the DNS server might have such a mechanism.