Yes, they have been pushing it for a long time. But its a major undertaking, so things take time. I think its just even more impressive that they have managed to push a decade long project steadily forwards. The latest memorandum that I linked even had a short summary of the previous initiatives:
> In August 2005, OMB issued M-05-22, Transition Planning for Internet Protocol Version 6 (IPv6), requiring agencies to enable 1Pv6 on their backbone networks by June 30, 2008. This policy outlined deployment and acquisition requirements. In September 2010, OMB issued a memo entitled "Transition to IPv6," requiring Federal agencies to operationa11y deploy native IPv6 for public Internet servers and internal applications that communicate with public servers. Specifically, the 2010 memorandum required agencies to upgrade public/external facing servers and services (e.g., web, email, DNS, ISP services) to operationa11y use native IPv6 by the end of FY 2012; and to and to upgrade internal client applications that communicate with public Internet servers and supporting enterprise networks to operationally use native IPv6 by the end of FY 2014
So that 2005 memorandum laid out groundwork to setup basic ipv6 backbone networks, and mandate purchases to be ipv6 compatible. That has been happening in the past 15 years so that now we are at the point that the latest memorandum is aiming to transitioning to IPv6-only deployments. If they set the requirement to be largely IPv6-only in just couple of years, then they must believe that there is good readiness for that at the moment, and I would like to think they have done their homework here.
I was on the IPv6 transition task force for a large federal agency (well, one of the military services) from 2008-2010. They don't take it seriously, don't fund it, there's no internal mandate or accountability around it, and nobody knows how the hell it works.
Like, the US Govt has been 'going to move to ipv6' real soon now since I was a baby engineer.