Well, lots of talk on mailing lists and so on, and I got the impression it was greyed out on mine because it runs under wine... But it seems the official comment is:-
Q: "Now that there is an option to use IPv6 addresses in World of Warcraft"
A: "No there isn't, it's just there for future use. There will be an announcement when it's ready but don't expect it soon."
Stop buggering about Blizzard!!!