With kingdoms up I can't help but think about the concept of legacy - bloodlines that continue after death and give a sense of unity to a social group, beyond mere usefulness.
Now, what if there was a way to make family lines valuable, so that players are encouraged to cultivate a single line of characters instead of grinding several alts through their gameplay? Or to flock around a legendary family?
One way I think this would be possible is through family-bound traits. Certain hard-to-bot actions (like completing quests or earning 10k/20k/30k etc XP ) would have a very small chance of granting the character a random trait (faster building speed, higher UA damage, unique crafting recipes, butchering quality raise, unique special actions, LP or FEP % boost). This trait would be permanent and would be passed down to the inheriting character after death. The upside of this is that one would only be able to acquire traits if they went outside did stuff instead of sitting inside grinding.
That in itself would be enough, I think. But it could be expanded further to motivate people to form societies. If two characters have the same amount of traits they could choose to unite their bloodlines, and the first of them who dies would then have a chance of inheriting the traits from both chars. Or maybe some traits could give mild buffs to all hearthfires within a certain range from the owner's hf, just like a mythical king would.