When it comes to multiplayer the way I'd like to see it done is to have it interwoven within the world and narrative as a whole, similar to how Dark Souls does their mulitplayer.
Where you could have factions and organizations IE Corporations, Nomads, gangs, cops, etc. During the story you come across these factions and if you wish to you can join their faction/help them, and doing so not only affects the single player world and how npc's see you but also opens up multiplayer and interacting with other real life players in your game.
So lets say you join the cops, you could then have access to a social space (IE police station) that you can enter and inside the game will seamlessly place other real players in that space, so it's kind of like a hang out for other players that joined that faction, you could maybe trade goods with other players in that faction, group up for specific faction missions together, etc.
Now the cops naturally would be enemies of gangs and criminal types of factions. Throughout the game there could be faction quests that would task you with an objective, and on the other side the players who are in opposing factions would be tasked with the same quest but against you. So it would seamlessly blend in other players within your world/quest.
To me this is the kind of MP I'd like to see, something that feels like it's part of the "world" and not something just tacked on (IE like a deathmatch mode or something).