IPv6 Backwards is Better
Designers forgot to take into account real-world issues.
Author Keir Thomas addresses the many issues facing technology with the rapid move towards IPv6. In his article on PC World, Thomas says although IPv6 has actually been around since the late 1990s, when it was created to supersede the older version 4 of the Internet Protocol scheme (IPv4), it was not designed backward compatible with IPv4, which would have made transition seamless for most organizations.
"It's because of issues like this that IPv6 is by no-means a shoe-in over the coming years. It may well simply be ignored. There are other ways of getting around the address depletion issue, such as carrier-grade Network Address Translation, where a neighborhood shares a single IP address. This is vastly inferior to IPv6 in many ways but it has the advantage that it's easy to implement, and that's really all that matters in the commercial world of the Internet. Additionally, there's talk of a commercial marketplace for IP address blocks arising in the future, and the buying and selling of addresses might provide an additional incentive to simply ignore IPv6.