> Depends how you define "without any reconfiguration".
Like this. I have my DNS configured now. I have my DHCP configured now. I have my static hosts configured now. I have my firewalls configured now. I have my services configured now. Without touching any of that (i.e. configuration), can I talk to IPv6 hosts out there? I'm guessing the answer to this question is probably no.
What DJB pointed out is that deployment of new software on all computers in existence is surprisingly easy (in fact, it happens all the time with updates). Deployment of new configuration is hard (each admin has to figure out their new addresses, firewalls, DNS, tunnels etc.). Ergo, IPv6 should have embedded IPv4 in itself. And because it didn't, we have the current interoperability disaster where hosts with IPv4 addresses cannot talk to hosts with IPv6 addresses natively.
Sure, eventually all this will be overcome and we'll all end up being on IPv6, but the plan was not very good.