I think there is a HUGE opportunity here for unique quests, dialogue, atmosphere, and rewards.
For example, take the Nereids. There are lore books which describe a priesthood that worships them, and some actively play a role in the conservation of natural environments, though the one in particular I am referring to is more of a "trickster spirit" bordering on malevolent toward those that threaten her sanctuary, there are others as seen in Arx Corinium that are actually willing to communicate and work together with human/elf races.
The point is though, it would be awesome to be able to attune with say the "nature" faction and gain perks like being non-hostile to Spriggans, Nereids and certain other creatures, even being able to talk to the sentient ones and sometimes get backstory or even quests. Or join the Vinedusk Rangers. Or become a disciple of the Two Moons.
Quests and rank could reward unique housing opportunities, costumes, furniture items, etc.