IMHO, the internic should not allow any domains to have pri+sec nameserver
in the same /24
Strictly speaking, you can't assume that "in the same /24" translates
to "share the same exit gateway." They *could* be /32s routed around
inside the interior of some provider with enough exit gateways and
such to keep them reachable in the event of failure.
The assumption would appear to be valid here, sadly.