If you have 10.000 zones, I can also be tricked into seeing a justification. I agree with Jeroen. We're having waaay more than 10.000 zones which (currently) don't go over the 512 byte limit.
On the contrary, if I wanted to get PI, what would stop me from taking one zone, expand it's dns records up to 512+ byte and request the space?
Why should address policy be so tightly tied to the technical details of the DNS protocol and its implementation? Are you saying that IPv4 Anycast is only justified if the application is DNS hosting and the number of separate zones (presumably you count SOA records) goes over a certain limit? No other application is justified? Only the organization hosting the DNS is eligible, i.e. a data centre operator who wants to provide hosting services is not eligible? Every DNS hoster with over x zones gets their own /24 even though you could aggregate over 200 such organizations into one /24 if they shared data centre infrastructure? It seems to me that this approach to IPv4 Anycast prefixes only reinforces an existing monopoly and blocks organizations who might want to take a fresh approach to DNS hosting or other types of application hosting. --Michael Dillon