they have already split the guilds up. for example, the Conjurer's Guild is in Gridania.
I don't believe the OP is referring to those kinds of guilds. In FFXI, for one, they did not exist though there were certain characters that started the quests to obtain certain advanced jobs so you might consider those a part of it.
Anyway, what the OP is referring to is crafting guilds where you would go to improve your craft level, take your test, and turn in items for the guild item of the day points. Oh, and buy limited stock of certain items the guild offered its crafters.