I don't know how much the lore allows it, but the part where it says "For centuries, this world slumbered uneasily. But it did not die… As glacial ages passed, kingdoms rose and fell out of sight of the gods." makes me think civilization therefor npcs are possible. It would really enhance the solo experience.
When I say quests I don't mean skyrim/witcher style complex quests. More like jobs, favors for the locals.
This is what I have in mind:
1) Meadows: The same way you come across abandoned villages you could come across populated ones, about 15-20 villagers. There you could earn the favor of the locals with bullshit like help us stockpile wood or food. Bring us a queen bee so we can make mead. You could also trade with stuff like 5 wood can get you a feather or 2 neck tail for a carrot soup stuff like that just to breath a little life into the game. You could also move in the village after a while and get better deals for resources. Raids could happen to the village, let's say arm them by getting them weapons, arrows. Build them a wall etc. Build a new house to someone, beat up the village strongman in a fistfight.
As you progress you could get unique quest according to your technology. Like if you have iron, you could get a quest to build the Jarl a house with at least lvl 10 comfort home or shit like that. The simple clear out that dungeon kill that miniboss quests for gold/resources/unique loot/gear could be great too. Or murder all of them for their stuff.
Rival or friendly villages could also be a thing. Hositle: raid the others, protect from raid, sneak in and steal stuff. Friendly: build a road from one to the other, protect a cart while it gets through the forest etc.
Also if you're caught stealing from them the get hostile.
2) Blackforest related quests, like little Björn wondered into a troll cave kill the troll escort him home. Hunters lost in the woods go investigate. Recover uncle Sven's gear from the Burial Chamber.
3) In the swamp you could find the remnants of the civilization that built the sunken crypts.
4) in the mountains, you could find some people stuck in one of those log cabins, they lack winter gear, firewood running out. Help them get out of the mountain. Either give them wolf capes or frost resistance potions.
The people you helped could be potential followers that behave similar to wolves but you have to feed them and gear them up. Or give you something cool like an enchanted sword a'la epic loot.
Sorry for the long winded post, I just had to share.
If not the game devs, modders might make something like this a reality.