For example, consider all the IP blocks registered to uncontactable
entities. I've seen various ARIN netblocks with comment fields saying
basically "ARIN has been unable to contact this address block holder;
if you have updated contact info, please tell us", rather than
deregistering the block. I've seen RIPE take similar (in)action.
and the legal basis for ICANN or the RIRs doing this?
I don't quite understand your basis for saying this, as though by
pointing out the problem I had somehow acquired responsibility for
laying out a detailed plan for fixing it. But that aside: this is
ICANN's problem, or rather, ICANN's lawyers' problem. (This is one of
a lawyer's functions, to figure out how to do what needs to be done in
a legally good way.)
To my non-lawyer's understanding, I'd expect this to simply be a
clause
in the contract under which ICANN/IANA delegates address space to the
RIRs, making this a matter for contract law - similar to whatever
arrangements are in place to pass responsibility down from the RIRs to
their assignees.