Not only can it be true I've done it at a conference, which is to say I've implemented an IPv6 only network for conference delegates and had zero connectivity c

Not only can it be true I've done it at a conference, which is to say I've implemented an IPv6 only network for conference delegates and had zero connectivity complaints. The ingredient you are missing is while the clients only talk IPv6, the gateway they go through (must) have both IPv6 and IPv4 addresses. There is a well defined mapping from IPv4 to IPv6 addresses, so if the IPv6 clients need to communicate with a IPv4 only host they use it's mapped IPv6 address. The gateway then NAT's all those mapped IPv6 addresses to it's IPv4 address. Which only leave the problem of does an IPv6 client know to use an mapped IPv4 address, given it is supposed to know nothing about the IPv4 world. The answer is you make it use a DNS server that lies. I'll leave it to you to figure out exactly how it lies, but it isn't hard to figure out given it has clients that only understand AAAA records, and some hosts (such as twitter) that only resolve to A records.