If you're thinking 'mod', you would be right! Via Skyrim Nexus comes this mod that fleshes out NPCs in Skyrim considerably. We're talking like, over 50 voice actors with almost 100 new characters AND new quests on top of that. You can marry eight of these new characters. Crazy stuff.
Of the 18 followers, 7 are being expanded to include commentary on every quest and location in the game, including bonus conversations during or after major questlines. Currently, these followers, whom I have dubbed "Super Followers" because they fly and wear capes, have approximately 500 lines each, with the ultimate goal of having thousands. However, any follower can be expanded, it simply requires a willing actor.
The size of the mod is over 1GB, and will only get larger. If anyone is interested in constructing smaller, child mods for specific followers or NPCs, you have my approval. Just beware that some NPCs are still expanding, and you will constantly have to add new content as I update.
If you watch the trailer above, you can get a sense of what this looks like in-action. It's clear that this is an in-depth mod, and it's only going to get bigger — right now, the mod is still a work in progress. You'd help it along if you reported bugs or anything like that after downloading (which you can do here). Even if you're not interested in bug-hunting, this still seems like a worthwhile thing to download though.
Interesting NPCs [Skyrim Nexus]