What is the harm in having societies that have mostly unlanded characters ? Who cares if some of the societies are similar.
You could even have a Knight Society that only knights can join from lords to hedge knights also.
There seems to be A LOT going on in Qarth they seem to have multiple landed societies the Ancient Guild of Spicers , Warlocks, Tourmaline Brotherhood and the Pureborn all fighting for control of trade and dominance within the city.
You could have a society for the cold ones religion where landed humans sacrifice other humans to the others to create more white walkers like craster did.
Ironborn could have a society that revokes the old ways no more reaving and raping as Daenaeys told Asha in the show that she had to change their ways its not like they are totally against it either because a lot of Ironborn don't reave anymore and one of the lords even converted to the faith of the seven.
Old Gods possibly a society that only people with greensight can join including children of the forest the children should have a landed location inaccessible to everyone else. So landed humans would be in that faction.
Rhllor only certain red priest have powers obviously so there should be a trait like greensight that would be used as a restriction to get into the society and they could assassinate people, bring people back to death, prolong life (red woman is old as shit) at higher levels lower levels usually just tricks with fire or looking into the flames and seeing visions in the form of an event.
Also for the harpy religion maybe the satanist version of that would be called sons of the harpy extremely xenophobic to foreigners murders them like the assassins in vanilla espcially if any harpy land is conqoured it intensify .
These are just some ideas idk how difficult they are to implement but im just throwing some stuff out there amazing mod so far and I will help with lore best I can for ideas for the societies im suggesting.
Because if the player is never going to be able to see the society, never join the society, never interact with the society, never be able to use any feature from the society then making it a society is completely pointless and just a waste of time to script.
We could have a society for literally anything, that doesn't mean it is a good idea. There is no lore basis nor common sense basis for a society of all Knights working together to achieve any sort of end goal, they are just Knights nothing more.
We could have a cold ones society (Ignoring the Old Gods Devil Worshiper one), but why do that when there is already the religion and the mechanics can be tied to the religion. Making it a society adds nothing of value.
The show is not our primary source of lore coupled with that is not what a society can do, that would have to be something like an entirely separate version of their religion as you cannot change what a religion can or cannot do mid game.
What secret society of Greenseers did I miss in the books?

And don't say Bran and Bloodraven, two people does not constitute a society
The landless red preists? Who the player will never play? Or Stannis joining the society of landless red priests and being the only landed members as he is one of the Lord's Chosen that they cannot all actually agree on cause some priests say it is Dany, some Stannis, some other random people most likely.
This is the problem with AGOT and societies, once you actually think past the cool factor of societies and look into what makes a good one AGOT has very few options:
- A society needs to be open to lords, it cannot just be landless or unplayable characters
- It must have a lore basis for a structural leadership of multiple tiers
- All members must be working towards the same goal or at least a common end game
- There must be missions which are clearly handed out by certain people to accomplish the above goal
- The society must exist with more than just a few people to be worth making
- The society must exist for more than just one tiny bit of the time period to be worth making
- There needs to be ranks, events, missions, powers and flavour all added in to make a society and that takes a long time to script
So in AGOT for societies that meet those criteria, there really are not that many even if we stretch some of those requirements or ignore the lesser ones. Off the top of my head the ones I would think of are the Alchemists Guild and the Iron Bank and maybe at a push one could argue that Lords trying to forge links as a Maester but we have only really seen a couple of people do that so making it an event chain would arguably much better.