Recently I've been talking about implicit sharing - the idea that players create and refine content as they play, and in turn that content is automatically merged into other player's worlds. I've also been talking about how that content needs to be something with emotional meat to it. It needs to be more than just a ship with specific stats - it needs to be a story, a character, an interaction.
There's not really any existing tools or approach to allow for that kind of development, so new tools have to be created.
My first stab at it is "recasting".
Any kind of game can use recasting, but it does require a very specific kind of play format. It needs to be:
1) "Open approach": issues and challenges can be approached via a variety of means. For example, social, technological, or physical. These approaches aren't simply pass/fail, but require time and multiple attempts in order to get success.
2) "Ally NPC": Players need to be able to create and direct allied NPCs to perform tasks, including open approach tasks.
3) "Enemy NPC": Enemy NPCs can be directed inside limits if compromised: convinced, threatened, seduced, coerced, whatever method.
These three concerns basically form a system where NPCs can interact with other NPCs in a repeated, prolonged manner. The system also allows for open-ended plot lines, since you can lay down a series of plot beats and let the player traverse them using open approaches.
The recast system requires all those elements, because the idea is that different players keep playing through the quest line, but from opposite sides.
It might be easier as an example.
You're a cop (A). There was a drunken brawl and it turned deadly. You're hunting for the survivor (B), who went into hiding.
Your avatar is nerdy, so you take a technical approach - tagging his phone, looking for credit card purchases, perusing security cameras. Your success is limited, so you call in a support NPC (C) - a social cop who is assigned as your partner. He gently interrogates barkeeps, relatives, known friends... and that approach gets more success. You eventually learn that he's staying at a friend's house (D). The friend is a big bruiser of a guy.
You can tackle this however you like, but that bruiser ally makes it dangerous to just pop in and arrest him. Since you've got a social ally, you convince the bruiser to help you safely arrest the perp rather than go in guns blazing or wait around for days for him to slip up.
Mission over. Pretty simple. Everyone gets XP.
Now the mission is recast.
The next player is a cop. You're tasked with defending a witness. You start with a partner - a big bruiser kind of a guy (D). Your avatar is a social cop, an investigator (B).
You quickly learn the details. A mafia agent is hunting this witness down. He's a nerdy sort of mafioso (A), so you expect he'll use technical searches. So you take proper precautions, largely going off-grid and getting people to help you out so you don't have to use phones or credit cards. Unfortunately, the mafia agent brings in a specialist, a greasy, fast-talking knifeman (C). They interrogate the people you were relying on, and seem to be narrowing in on your position.
You decide to go on the offensive. You try to talk to the nerdy mafia lead, looking for information or even an outright ally. You don't realize that the knifeman is threatening your partner even as you speak. Even as you're trying to convert his boss, their social goon is doing the same to your team. You never realize the partner you left behind to guard the target is being compromised.
In the final, climactic scene, you are betrayed by your partner. But the mafia leaves you alive, since the nerdy lead has come to like you. You're sure she'll show up again some other mission - all these characters will.
Mission over. Everyone gets XP.
Now the mission is recast.
The next player is a cop. You're tasked with hunting down a pair of killers. You built a big bruiser of an avatar (E), and your partner is a nerdy guy (A). You decide to hit the streets - you track and intimidate the people who might know anything, and quickly get a bead on the targets. They were using social techniques to stay off-grid, but your techniques didn't involve the grid.
The two are a slick, dangerous "dame" (B) and a knuckledragger (D).
On the second day, another cop approaches you. A social specialist with a good record (C). He tells you that he was assigned this case with you, and that you should work together. He says he can convince the knuckledragger to fold, although you can tell him not to. Even as you're working this out, your partner is being seduced by the dangerous dame... do you notice in time?
You might have figured out the basic algorithm.
See, the NPCs don't really have any algorithmic personalities or behavior. But you give them commands that make sense for them - do these things, interact in these ways. Then the next player plays from the opposite side. Even as they give their own side commands that make sense, they see the NPCs you originally commanded doing the things you directed them to.
This isn't quite the same as two players directly opposing each other simultaneously. Each player is playing a one-player game. But the NPCs remember and continue to act. The steady drift in the situation as more NPCs are introduced and refined introduces a feeling of personality.
For example, at this point there is a dynamic where the social defender (B) seduces the technical offense (A). As more characters are added and the situation changes, that behavior may not make a whole lot of sense. In some cases, one or the other could even be recast as a player character again! But the two characters are now locked together by "fate": the technical offense "wants" to be seduced by the social defender, and the social defender "wants" to seduce.
So even if you are the social defender and choose a radically different approach to the setting, the instant you meet the technical offense they will fall in love with you. Similarly, if you play the technical offense, you're not going to be able to resist the social defender, no matter how good your stats are. That's your personality.
It's also important to consider continuity between missions.
No mission starts clean. All the characters you created for last mission are used in the roles of this mission. The very first player - he created a social partner (C). That social partner will be recast into another social specialist role in the next mission, and in the mission after that. This leads to tense moments where your long-time allies are caught in a dangerous web. Enemy NPCs work the same way.
In a different setup, it'd make sense for it to even be player-linked. That dangerous dame might be the funhouse mirror version of the player that created her, and therefore her progression and activities could reflect that player's ongoing activities. That player could even find that there is a funhouse mirror version of you in their world, reflecting your behaviors and actions.
Anyway, as a first stab at a system, this seems like it'd work. I haven't built a working prototype yet, though.