The main advantage of IPv6 over IPv4 is the huge 128-bit wide address space. As an example you can have up to 2^80 devices with public IPv6 addresses at home in contrast to IPv4 where you usually only have one public address.There is no need for address/port-translation, just simply plug the Arduino(s) with ipv6EtherShield into your home network and have access to them from all over the world.