That is the only conclusion I can draw as they have a number of realms not working on IPv6 at present, and still have the setting default to unticked.
IPv4 addresses have run out, and already ISPs are struggling with messy systems like Carrier Grade NAT. IPv6 is the current version of Internet Protocol and once again brings the Internet back to the way it was designed. For gamers this means less messing with the traffic, either by their own router, or systems within the ISP.
Looking at this in more detail, and looking at a similar forum post from someone else back in October, it seems that they are using SLAAC assigned (MAC based) IPv6 addresses for servers. This is just lazy, and means that any change of hardware can cause the address to change. I can only assume that has happened and they have failed to update server IP lists or DNS to use the new address. They should probably manually assign IPv6 addresses.
If it had been the IPv4 address not working, they would find a way to fix it.
12365247226 and 12844094863.
It is a real shame. I was impressed when they launched IPv6 support a few years ago. They were ahead of a lot of people. Now we see FaceBook, Google, and lots of content via IPv6. Even large ISPs are finally planning IPv6 deployment (A&A did it 12 years ago). The Internet is finally growing up, except for Blizzard. Poor show.