It can be hard to set up IPv6 for a relay, we're working on a grant to make it easier.
It could be helpful to do a request/survey to relay operators to find out their experiences. That is those who have ipv6 configured what was the process and if there were any problems in the process. For those who haven't yet configured ipv6 what is the barriers preventing them from using ipv6.
For me it was a problem at the ISPs end then it wasn't clear how to get network config to use ipv6. I got the shits with it in the end and just used iface eth0 inet6 dhcp. It works... LOL
Paul