There's literally nothing stopping a moderately skilled IT team from integrating ipv6. You can run any site easily using both. The exceptions are few and even those aren't that hard to deal with.
Source: been running dual ipv4/ipv6 Web servers for over 10 years (maybe 15 would need to check) . Likewise had ipv6 dual stack at home for a similar amount of time, initially using tunnels and then native.
Almost every server provider will give you ipv6 for free. There's really no excuse these days not to run your services on both protocols now.