One non-security (well almost) reason is that RIR and other
allocatiors of large address space are required to list in-addr
for the parent block, because thats how they delegate down to those
who do chose to provide in-addr.
So a consequence of not having in-addr for a given /prefix is
that the parent /prefix-1 has to wear repeated requests for in-addr
which it can't answer, and while this is not a big deal inside small
allocations, for shorter prefix owners (or registries) the load
can be excessive.
Its a non-deliberate DoS effect that chokes semi-core DNS servers.
We wind up doing nasty things like pretend-revoking the delegation
so we can answer the much shorter NXDOMAIN instead of ourselves spinlocking
to find an answer and timing out.
So, I would welcome a requirement because it has the effect of reducing
load on central infrastructure, and risks of DoS or service-quality loss
to a third party when a large network space is live, and causing widley
distributed places to attempt in-addr lookup.
cheers
-George
