On the other hand, switching the "default" meeting SSID to IPv6-only/NAT64 while still providing the dual stack network as a fallback, preferably combined with a helpdesk staffed by volunteers ready to analyze any problems that attendees might have, strikes me as a pretty good opportunity to raise awareness and to find problems where further work is needed.
From a host perspective, NAT64 directly on wifi is not attractive: it will require an address translation component in every host to deal with legacy applications that handle IPv4 literals.
NAT64 is also not attractive from a backward compatibility point of view: IPv4-only devices and hosts that are dual stack but lack the 464XLAT component will fail. Considering those issues, why does it make sense to subject attendees of a RIPE meeting to such a network? Anybody who wants to test can do that in the current setup. Why trick other people into connecting to a network that they are unlikely to encounter anywhere else?