This may be more complex than other games. They have to contend with everyone in the guild and the other guilds that they may be a part of. Also the cross server thing may be an issue as well. The fix would be that everyone except the leader, leaves the guild. This might make it easier and quicker for the Devs to offer the guild name change. and then re-invite everyone after the name change.
Or. . .
It might be real easy for them to do and they are just waiting for more people to want it so they can drive up the value of the option.
Either way, I hope this happens soon! My money is getting impatient! 
stripped of will and soul, only
their thirst for freedom gives them hunger for vengeance…’
their thirst for freedom gives them hunger for vengeance…’