Internet6 statistics have just rised up to 16% and therefore quite close to the 20% where we consider IPv6 as a mainstream technology. Many countries are already there too.
April 2017 stats show how significant IPv6 massive deployment is worldwide.
The per-country adoption table confirms Internet/Digital leading countries are at the top too (in bold letters countries with a significant increment compared to March 2016).
One of the key deployments in the past year has been performed by India, rising up to almost 20%. Due to its massive population and Internet penetration at this point it is a cornerstone of IPv6 standardization as the main Internet protocol.
Other countries where IPv6 was surprisingly not relevant in terms of end users are starting their way finallly. This is, for example, the case of Spain where it has been under 0,15% during years and it has rised up to 0,35% in a few days.