Good news for those guilds who want to move to a new realm -- Blizzard will soon allow the ability to transfer the guild and its structures easily with a guild relocation service.
It appears that there won't be a single massive "transfer my guild button" that moves everyone over all at once, but instead, each guild member will have to pay their own way over to the new server. Once they get to the new server, all their guild bank, guild reputation, and so on will be over there.
Blizzard's full statement is as follows:
We want to give everyone an early heads-up regarding our plan to implement a guild relocation service for World of Warcraft. The idea is for a guild leader to be able to transfer a guild to another realm. The guild structure remains intact, including the guild leader, guild bank, ranks, and guild name (depending on availability).
Guild members who decide to relocate with their guild may initiate their own paid character transfer. Upon a successful transfer they will automatically be part of the guild when they first log into the new realm. Their guild rank and guild reputation will be intact.
Guild leaders who do not want a change of scenery may also choose to pick a new guild name using another new service. These services are in development and we will be providing additional details at a future point in time.
As with all of the features and services we offer, we intend to incorporate the guild relocation service in a way that will not disrupt the game play experience. Please note that this feature will require extensive internal testing, so you may see bits and pieces of the service appear on the public test realms.