I think it refers to the practice that companies like Facebook are using of not running IPv4 at all. All their systems are IPv6-only with the exception of their edge servers. They simply removed IPv4 networking from all their internal servers, desktops, engineers dev stations etc. That way developers and architects don't have to worry at IPv4, test everything twice, worry about attack vectors using the other protocol etc. They just have to make it work on IPv6 and let the webservers translate it to IPv4 for those users who still have IPv4-only connections.