Names and homes for all NPCs. They don't necessarily have to talk to you. Nothing gives me a "let's kill these anonymous piles of bits just for the hell of it" response faster than someone named GENERICPERSON or somesuch. And that kind of reaction is a prime example of a break in immersion. Massive crowds are not necessary to make a believable city.
Right......., except for beggars, thieves, street urchins, traveling mercenaries, random guards, servants/slaves. Many, many people in TES don't have their own homes in a given city, therefore, they should at most just be a name. If they actually have something useful to say, we should be able to talk to them. If not, then they should just be labeled or randomly named. Do you really care about the name, backstory, and dialogue every random street urchin child who pickpockets you and runs off? Or every beggar? Or guard? :confused:
The devs should devote time and effort into the NPC's that matter, and add more generic ones in addition to them. If Radiant AI can handle having all NPC's in a city having personalities and
meaningful dialogue, great. I highly doubt that would be a wise allocation of resources for Skyrim, however.
Also, I hope you don't get the same "kill frenzy" when you walk down the street in real life and don't know everyone's name and address.....cause that would really break the immersion when you're sent to prison.