support running behind NAT64?
Minor use case: running kresd on a machine without native IPv4. (maybe)
While DNS servers tend to have much higher rate of IPv6 support than (say) HTTP servers, there are still problems, e.g. Fastly CDN is a long-standing example that doesn't have any IPv6 glue.
So far one wants at least improve NS selection algorithm by:
net.ipv4 = false
or work around the problem by forwarding to someplace with native IPv4.