Most "real" providers have diverse nameservers. For them,
Correct. But diverse announcements are neither a necessary nor sufficient condition for diverse namespace. And given you can't (in Europe anyway) get diverse announcements from day one, and you said...
IMHO, the internic should not allow any domains to have pri+sec nameserver in the same /24
...your proposal would exclude people with valid subnetting plans but no diverse announcements who wish to register new Internic names. Given Internic's current situation with lame delegation, I think this is the least of their problems. If you wanted to fix this correctly, you could find the penultimate hop to each nameserver, and check they were different. This would seem to be closer to what you are intending to achieve. -- Alex Bligh GX Networks (formerly Xara Networks)