This is part of my series on (Trying to) foresee IPv6 deployment.
Google is doing a lot of things for IPv6 adoption with its IPv6 program. First, it brings credibility to IPv6. When Google talks, the world listens. They have hosted a workshop about IPv6 adoption, where at least two important points where made:
about 0.5 % of internet users have a broken IPv6 connectivity, that is their computer thinks it has IPv6 connectivity, if presented with an IPv6 address, the computer will try to use it, but it will ultimately fail. Depending on your view, 0.5% may be acceptable or not (not acceptable from the point of view of Google)
T-mobile USA brought steam to the NAT64 approach by saying this was their way, and by putting some hard figures about NAT64 brokenness on the table.
However, as an ISP, for your clients to use Google (and affiliated sites like Youtube) over IPv6 by default, you need to have a special agreement with Google. This is because of the 0.5% that Google doesn’t want to lose. The point is that, for now, most ISPs still have a stock of IPv4 addresses, so their new customers have a dedicated IPv4 address to get the best possible connectivity. For these ISPs, there’s absolutely no incentive to enter into the agreement with Google. On the other hand, if IPv6 access was enabled by default, it would move large amounts of traffic to IPv6 for the ISP customers that have IPv6 enabled, pushing the ISPs towards IPv6.
All in all, I think the current Google policy of “IPv6 on agreement” restrains rather than encourages IPv6 adoption.