* Paul Vixie:
first, ARIN does not currently consider routability when allocating address space. non-routable space comes from ietf/iana, not the RIRs. so, for ARIN to start allocating nonroutable space is a big change. we would have to define "routable", we could face implied liability for routability on "normal address space"
Why? There is a technical difference between the two offerings (separate address spaces). It seems to me that this criterion is completely sufficient. It's up to the requestor to decide which type they need, and to make sure that the meet the published requirements. On the other hand, the IPv6 address space is so large that any entity can pick some prefix and use it to implement its own ULA registry. If there is real demand for such a service, that demand itself will make sure that the prefix won't be used for any other purpose. (".local." could be seen as a counter-example, but I believe the initial problems have been fixed by now.)