> How can you blur the line? It's either online multiplayer or it isn't, there's not really an in-between. You can't "kind of" have other people connected to your game. They're either there or they're not.

Dark Souls does precisely this in a fantastic way in two major mechanisms. The first is the shared player "graffiti", wherein players can write messages that are then propagated into others' games. The second is the shared "death ghosts', which play back a player's last moments before death in others' games as a ghost you can't interact with. These make the game feel like you're playing with others in a large world without having to actually put you in the same instance.