China has effectively mandated IPv6, and IPv6 certainly is popular in China (I think all mobile phones in PRC use IPv6, I may be wrong) - but let's not forget that China is promoting IPv6 because APNIC's allocated IPv4 space for China was comically undersized.

Unfortunately this is not the fact. While some ISPs are experimenting with IPv6, the vast majority are not on that train. Indeed, IPv4 address space has practically run out in China already, but many ISPs are taking the nasty NAT-like approaches, Carrier-grade NAT [1] for example. And it is particularly common in mobile. So far, IPv6 is only (relatively) well accepted among universities (CERNET [2]).

[1] https://en.wikipedia.org/wiki/Carrier-grade_NAT [2] https://en.wikipedia.org/wiki/CERNET

The Great Firewall likely affects the reliability of everybody's stats, but China seems to be way behind the US in terms of IPv6 deployment. (<3% versus 30%):

- https://www.google.com/intl/en/ipv6/statistics.html#tab=per-...

- https://stats.labs.apnic.net/ipv6/CN vs https://stats.labs.apnic.net/ipv6/US

Nope. If mobile network uses ipv6 then people would have no problem accessing Facebook

You do realize how firewalls work, right? You have iptables and ip6tables. Sure you need entries for both, and sometimes ISPs forget, but it's easily implementable in all major routers and operating systems.

Firewall rules are not yet implementated on ipv6 network in China by ISP. It is a fact, and actually people are using ipv6 network as a means of bypassing the wall.

And everything else would have slowed down because of resources (human and other) devoted to ipv6, and the complexity of ipv6.