It looks like ARIN, the US IP-registry, will be running out of IPv4 address-space by the end of the year. With only 3% of traffic being IPv6, with the US on the lower side, there will be an enormous challenge to speed up migrations/implementations of IPv6.
I am afraid more effort and money will be invested in large Carrier Grade NAT (CGN) solutions than in actual implementations of IPv6. Besides ISP’s being late, also here in the Netherlands, there are some large application and infrastructure service providers which are also behind. Amongst them are providers like Skype and Amazon Web Services, no small kids. If companies like this are going to support native IPv6, instead of some loadbalancing trick, traffic will rise very quickly.
I understand implementation cost can be high which I thinks is only partly true for Skype and AWS, but ISP’s seem to have a hard time getting CPE equipment that supports IPv6 in a stable manner. Implementations within backbone- and core-networks are growing, but the access-layer seems still to be a headache.