A potential path to IPv6 (again), but probably not a realistic one today
In practice, adding IPv6 to existing networks is a lot of work and is clearly going quite slowly in many places, or even not going at all. Given the economic incentives involved, this is no surprise; currently IPv6 primarily benefits people who are not on the Internet, not people who are. So what will drive adoption of IPv6, so that it becomes available in more areas? In particular, what would push us towards adding IPv6 to our networks?
My current answer is that the only thing that would really make this important is a noticeable amount of IPv6 only websites and other Internet resources that people here wanted to reach. If this happens and especially if it's increasing, that would create an actual win for our users for us deploying IPv6 instead of the current situation of it just being kind of nice. But where are these IPv6 only resources going to come from?
My best guess is that the most likely place to develop them are areas with large IPv6 penetration today. If you're building a business that is primarily or entirely targeting an IPv6 enabled audience (if, for example, you're targeting mobile users in a geographic area where they all get IPv6), only going with IPv6 for your servers and so on may make your life simpler.
Unfortunately there are a lot of holes in this idea. Even if you're dealing with an area where IPv6 is better than IPv4, running a dual stack environment is probably easy enough that it's cheap insurance against needing to expand into an IPv4 audience (and it means that all sorts of IPv4 only people can at least check you out). Going dual stack does increase IPv6 usage on the whole, but it doesn't turn you into an engine driving IPv6 adoption elsewhere. Beyond that, the Wikipedia page on IPv6 deployment and APNIC's numbers suggests that I've significantly overestimated how many areas of the world are strongly IPv6 enabled at the moment. If there's no real pool of IPv6 users (especially in areas that are not already saturated with IPv4 address space), well, so much for that.
All of this does make me wonder if and when large hosting and datacenter providers will start effectively charging extra for IPv4 addresses (either explicitly or by just giving you a discount if you only want IPv6 ones). That would be both a driver and a marker of a shift to IPv6.
(I wrote about a potential path to IPv6 a while back. This is kind of a new version of that idea from a different perspective, although I had forgotten my old entry when I first had this idea.)