The IPv6 designers refused to define an IPv4/IPv6 gateway, because it’s a contradiction to the NO-NAT, End2End paradigm of IPv6. The result is that IPv6 doesn’t really lift off, because every IPv6 user has IPv4 too (Dual Stack), which gives no pressure to move on to implement IPv6.
Large providers had to implement NAT instead of IPv6 to give their users connectivity, because NAT implemented a solution to address exhaustion now. If there has been an NAT64 gateway right from the start, we would have IPv6-only on our smart phones now instead of 10.x.x.x. That would give End2End capabillities at least for IPv6.
To test and show the current status of IPv6, I’m running an open WLAN hotspot with IPv6 ONLY. The access point is located in Wien, Rudolf von Alt Platz with the SSID AKK-IPV6ONLY.
I will add an IPv6 Only + NAT64 hotspot in the future.