Of course they can't. But the point is that if a client wants to interact with IPv6, they only have to upgrade themselves, and not wait for everything in betwe

Of course they can't. But the point is that if a client wants to interact with IPv6, they only have to upgrade themselves, and not wait for everything in between to get upgraded. And the service can serve on their IPv4 gateway and then pass the traffic back to other hosts to server IPv4 clients.