Thinking off the top of my head…
Is there a sensible way of sharing the cost of the necessary infrastructure upgrades around the world that doesn't invite gaming?
The real problem seems that the address shortage has yet to affect large parts of the service providers - the US can probably survive with its IPv4 addresses for another 1000 years (famous last words!). I suspect governments are reluctant to require IPv6 deployments partly out of consideration of the costs (anti-competitive); lack of technical skills (both in companies and regulators) and ignorance and possibly even because IPv6 is far from perfect. Quick fixes with layers of NAT are so much more inviting.
I wonder if, for example, the EU mandated IPv6 capable equipment for (imported) switches, routers, et al. whether that would have a similar effect on the industry that standards power consumption in stand-by or vehicle emissions have had. Once the endpoints can handle dual-stack then network upgrades can be handled with a minimum of disruption.