Even among the top websites, there are a <i>lot</i> of them that don't even do dual stack. Let alone IPv6 only. (e.g. Twitter)<p>Also, only using IPv6 is cutting out 75% of the world population, according to Google. <a href="https://www.google.com/intl/en/ipv6/statistics.html" rel="nofollow">https://www.google.com/intl/en/ipv6/statistics.html</a><p>However, public-facing dual stack but internal IPv6 only is done at e.g. Facebook IIRC (see <a href="https://code.fb.com/?s=ipv6" rel="nofollow">https://code.fb.com/?s=ipv6</a>)