For DNS to be usable, folks have to permit TCP DNS to work. I know of
some service providers that filter TCP DNS connections. UDP packets are not
big enough for many responses from an whois-type request.
TCP fallback is part of the DNS protocol. Any provider who blocks it is
already losing. We don't need to pay attention to them in the design, they
will fix their nets or they will lose more than they already are. Not our
problem.