Well, in Oblivion we've already seen that the capital city of the vast and powerful empire has a population of..... 26 - so by logic Skyrim can't have any cities with more than that
Seriously though - I'd like to see Assassin's Creed style cities. They were extremely immersive despite the people being randomly generated. I don't need every single person to have 10 lines of dialogue.
http://www.uesp.net/wiki/Oblivion:Imperial_City_People
And the Assassins Creed style, besides being IMO very innapropriate for the style of game, plain wouldn't work in ES because of the way NPCs are made and have to interact with the player, and give quests and such. People in ES are people, not scenery. You can't pickpocket someone in Assassin's creed and if you kill someone, another identical person takes their place. In AC, you can't walk around, talk to a few people and end up with a quest. You'd have to talk to thousands before you found one that was more than a piece of scenery. You can't talk to them (except specific mission ones) at all and they have no names, because they are not even real objects, they are just minute programs that run randomly at random points.