Note, that if you have registered "a.b.c." with "a.b.",
and somebody is resolving a name "www.anssi.foobarabc", a query can be immediately
satisfied without delegation when it arrives to the DNS server at "a.b.c.". If all
subdomains below "a.b.c." referenced in "www.anssi.f.o.o.b.a.r.a.b.c." are local
to "a.b.c.", then they can be specified in the one and only zone file for "a.b.c.".
Additionally, note that although there will now be much more domain components
in the names than before, it will probably not add much to the number of delegated
subqueries in global statistics. The more queries your name server answers, the bigger
part of the single letter hierarchy it will learn to cache. The single letter domains
should have a long TTL. When your name server has answered order of alphabet_size^2
queries, it has probably cached most of the second level domains (a.a., a.b., a.c.,...z.z.).
When it has answered alphabet_size^3 queries, it has cached most of the third level
domain DNS IP addresses.
To make sure that this learning process is not interrupted
too often, it would probably make sense to keep a disk based cache of the letter
based root delta domains. And have a guideline specifying a minimun TTL value that
the single letter domains must advertise.