This sort of thing is a big problem with IPv6 adoption. There's a lot of churn in internet software, server software, and hosting providers, and often many of t

This sort of thing is a big problem with IPv6 adoption. There's a lot of churn in internet software, server software, and hosting providers, and often many of the new guys delay IPv6 support in favor of other features. That makes it very possible for IPv6 adoption to stall or even reverse depending on the success of different hosting providers and software. Imagine a worst case scenario of a next generation web server which becomes hugely popular but which doesn't support IPv6. Fortunately that's an unlikely scenario, but unfortunately it can't be entirely ruled out. IPv6 is still a "nice to have" feature, and has been since it's introduction, that's always been it's major weakness.