The last v6day was an isoc effort, there can be a separate nanog effort or your own.
It does make a lot of sense for NANOG (perhaps jointly with RIPE and other NOGs) to organize monthly IPv6 days with a theme or focus for each month. If you have a focus, then you can recruit a lot of IPv6 testers to try out certain things on IPv6 day and get a more thorough test and more feedback Skip July and August because it takes time to get this organized, and then start the next one on September the 8th or thereabouts. For instance, one month could focus on full IPv6 DNS support, but maybe not right away. A nice easy start would be to deal with IPv6 peering and weird paths that result from tunnels. That is the kind of thing that would work good with a lot of testers participating and an application that traces IPv4 and IPv6 paths and measures hop count, latency, packet loss. In conjunction with the monthly IPv6 day, NANOG should set up a blog page or similar to publicly collect incident reports and solutions.