Would this work?

You decide on what kind of faction it will be, choices are

1) pickpocket/thieving
2) slavery/smuggling
3) mercenary/hunting
4) exploration
5) magic
6) assassination
7) 1 and 2
8) 1 and 2 and 6
9) 1 and 6
10) 2 and 6

These are just examples. Anyway, once you decide this, you are free to build your faction building. This is done in the same manner as the build your own home mod but on a slightly bigger scale, the building will be different based on the choice of faction you made.

You are then free to find npc's to join the faction. Some good citizens won't join theives/assassins etc. you can then assign a rank to each member. You are guild leader, you can have one person just below you. Two below them, three and so on until you reach the bottom of the ranks. A guild leader you can assign missions to each person, certain missions can only be given to certain ranks. Lets take mercenary/hunting faction as an example, A second in command won't take small radiant quest to go and kill a bear, but the low ranking members will. You gain items/gold from the faction reward chest. You can fire members and rehire new ones to fill the gap and you can demote your right hand man and promote a lower rank for example.

A lot of quests would have to be written, big quests and radiant quests for each faction type. I'm not sure how workable this mod is. It sjust something I would love to see and if I had more than very basic modding skills I would work on it myself but I know enough to know it will take an experienced modder to make this work to its full potential.