IPv6 end-user deployment in the US will be far ahead of 32% by 2019.
To get 32% users with IPv6 worldwide they've conservatively assumed quadratic growth continues instead of a more typical S-curve technology adoption. Using the same quadratic assumption for the US projects IPv6 end-user adoption there will be about 85% by the start of 2019. That is probably an underestimate for US mobile operators as VZW is already over 70% and T-Mobile US is over 50%.