When a IPv6 only host wants to reach a IPv4 only host, why does the DNS server (or possibly the NAT-PT gateway?) have to rewrite the A responses to AAAA?
Couldn't IPv6 simply embed the IPv4 address in the destination field of an IPv6 packet (e.g. by simply prefixing it with zeroes or some other, well-known prefix), and leave it to the default gateway to do all the translation?
I don't quite understand the motivation for DNS64.