5% of Google's traffic these days and growing on a hockey stick: http://www.google.com/intl/en/ipv6/statistics.html . My Comcast cable Internet comes with a native IPv6 block.
IPv6 requires not just the endpoints, but the routers in between to be on board with it. HTTP/2 only requires end-points. There's a lot less friction for HTTP/1.1 -> HTTP/2 upgrades than IPv4 -> IPv6 upgrades.