GitHub does not support ipv6
ip6.nl
ip6.nl
However I would imagine the likes of Netflix and Github to be a little more cautious about changing their setup. The real people to nag are the local government websites. These are often low hanging fruit that just don't change because they don't get paid to be proactive.
In practice, it makes sense for the largest bandwidth users to move first, because that means ISPs can deploy IPv6 in order to reduce the load on their NAT infrastructure. (And most ISPs will be using NAT sooner or later, because giving everyone their own IPv4 address is simply not sustainable.)