> You have some Joe Sixpack on IPv4 now. He simply cannot use IPv6 network. And why? Because someone decided that he needs a new address, when he's got a perfectly valid one.
Sorry, but that's bullshit. Joe Sixpack's computer will *automatically configure itself* to start using IPv6 as soon as it's attached to a network which supports it, similarly to how it automatically configures itself to use IPv4.
Mr. Fancypants System Administrator might have to change *his* configuration to get all his services talking IPv6 (he probably has custom firewall rules, has services listening on specified some subset of IP addresses assigned to the host, etcetc), but Joe Sixpack most certainly does not -- his OS just supports it out of the box, and will magically start working.
Getting everyone using routers with IPv6 support is the tricky part. But that's required no matter what!