Thus spake "Brian E Carpenter" <brc@zurich.ibm.com>
Fred, the point is that ULAs should be unambiguous, so that if they happen to meet (e.g. via a VPN, or following a merge of two previously separate networks) there is no collision. Currently ULAs include a pseudo-random prefix, which leaves open a theoretical possibility of collision. Centrally-allocated ULAs would not have this issue.
The chance is negligible until you have a number of organizations interconnecting that approaches the AS count on the public Internet. Those who are uncomfortable with those odds can get PIv6 space. ULA Central does not solve any problems that the existing tools already solve, and it creates new problems of its own. S Stephen Sprunk "Those people who think they know everything CCIE #3723 are a great annoyance to those of us who do." K5SSS --Isaac Asimov