ARIN is missing another way to re-claim and re-home IPv4 addresses. There are companies and schools who have ALOT of excess address space in the form of A and, mostly B blocks. If the registrars reviewed the allocated blocks and required those holding the large blocks to justify keeping them they would get a large number of address blocks back. Most people are using NAT internally so the B blocks they got years ago are no longer needed. But of course they have no incentive to return them. While this proposal might help, from my experience I'd say ARIN did not require good justification for allocating B blocks in it's infancy and that is now contributing to the lack of free address blocks.