IPv6 in the DMZ
You don't need to rip 'n replace all the IPv4 stuff. Most networks use the 10. 172, and 192 private IPv4 blocks internally and only ever worry about real IPv4 addresses in their DMZ.
You simply add IPv6 to those few machines in the DMZ and you are pretty much done.
I believe various network kit vendors EG: F5 supply application layer gateways/proxies in their offerings. As long as your boarder firewalls, load balancers etc can do IPv6 and of course your upstream provider you are golden :)