I've tried this post a couple of times now - and it always begins to wallow.
I want to say first that the social contract in a game does not depend on the DM. All the various things I've written about DMing - pacing, focus, mind-fuckery, trust - are there because we have no alternative to someone acting as judge, intermediary or interpreter between the players and the world.
The DM has to make decisions about what is possible, because the rules cannot account for every idea or innovation that occurs to a player in every situation that might occur. The gameworld is too complex and multi-dimensional to ensure every contingency is managed. This is the 'judge' aspect. Still, I make very few new judgments in a given game. Most of the time, I am reminding players of judgments I've made in the past, which I've remembered or the players have forgotten - or the players are reminding me, because my memory isn't perfect.
If we had some sort of device - let's call it an Interpolator - that could remember all these judgments and keep track of them, along with the remaining rule structure that has already been put in place, that could ease my burden considerably. Once in place, we could agree as a group to modify the Interpolator occasionally only for new things. This could be done as a group. No single person would need to do it, though one person in a group may be more imaginative/creative/aware of issues that came up. Once the new idea was logged in, however, the Interpolator would handle it.
We could then apply the Interpolator to the mechanical elements of the game. Not only would the Interpolator know what die needed to be rolled or what the results were, it would not be necessary to roll a die at all. Once the player decided to do something - stating the player's intention - the mechanics of 'effect' would be managed and the result would be instantaneous. This would massively increase the pacing of the game, since all the mechanical detail would be eliminated and made faster.
The DM's second contribution, the intermediary, mostly works as describer for the players. The room looks like this, there are this many people on the street, the sun is going down so there is this much level of light, etc. There's also a considerable element that the non-player characters in the setting talk like this, they have these agendas, etcetera.
Obviously, an Interpolator could handle all the imaginable visual details. It would be clear how deep the chasm was, how long the road was, how green was the grass and so on. Once again, this would massively remove a lot of burden from me. Since this would also be linked with the mechanical aspects of the game described above, the players would be interacting with the environment in real time, so that in game/out of game elements of play wouldn't be necessary. The focus of the players would be on what they saw. While yes, they would probably still joke around and make mock of things, now they would be doing it while standing in a forest or visually seeing the NPC standing three feet away, giving them cues that the NPC could hear and understand what the players were saying (and making judgments about them). This situational awareness would considerable cut down on the amount of inter-player dialogue (tell the guard he's attractive) that goes between players, as they would be aware that such dialogue was being overheard. This would greatly cut down on meta-gaming and vastly increase the immersive quality of the game.
Probably, the non-player characters would be necessarily simplistic, at least for a time. Still, there could be formulas that were designed to let players 'teach' the closer non-player characters how to act. So that if the character told a friendly NPC to stay behind the party and use their bow, rather than running into the fight, this would become the default action of the NPC. The next time the party battled, the player would turn to tell the NPC to use their bow and see the NPC pulling out a bow already. Or the player could give some other order to the NPC and these orders together would be managed to encourage a sort of contingency program that NPCs would follow.
Non-friendly NPCs might have a wide range of programmable elements that could give them 'character.' It would be best if this were accessible to the players, however. Corporations, no doubt, would sell characters, but ultimately some sort of youtube-create-your-own-content would be far stronger in the long run, since tens of thousands of individual creators would be more imaginative than oh, say, Mike Mearls. If it got online, we could fill our towns and worlds with characters stolen from the net - and even if many of these characters were duplicates in behaviour and purpose, for the most part in most games they already are. Made individual personalities for thirty attacking orcs, lately? Hell, if said orcs had two random personalities sprinkled between the 30, we'd be stunned. In any case, there'd always be room to tweak a personality very slightly - and everything we did would be remembered and automatically carried forward.
This might mean starting up a game and suddenly watching NPCs randomly killing NPCs, like spontaneously mixing a base and an acid without realizing the result - but such things could be planned for (and noted, so that it didn't happen again). In any case, no single player would need to be 'the DM' in this emplacement . . . a group could decide how to seed a town with individuals or simply let the Interpolator do it.
The DM's third role, that of interpreter - well, we've already covered a lot of that, haven't we? I wouldn't need to explain rules or explain the motivations of the NPCs because it would be right there in front of our eyes. I wouldn't need to mind-fuck the players - just being in a visual environment that was full of sensory information would manage to make everyone feel overwhelmed and out of their element. Most of the mind-fuckery is immersive in its intent and the Interpolator - even operating at a pretty dumb level - would do that nicely the first time the player encountered an actual door with an actual uncertain, visual possibility behind that. So I'm off the hook there, too.
And as far as trust, well . . . this is interesting.
Most legitimacy is established by making sure all the players are treated equally. But the Interpolator does this automatically.
Consider the trust between players. Jim, Wilma and Quentin all must make decisions that will keep them alive individually and alive as a group. In a normal game, Quentin looks down at his character sheet and sees only that - his paper. He looks at Jim and Wilma and sees them as people sitting at a table, perfectly safe in the face of three orcs, so it is all a game to him and he is free to treat it as a game. Having this freedom, he can quickly justify the game's lack of personal meaning by reducing the immersion he feels and can from there begin to fuck with the other players, breaking down the social contract.
However, if we are visually seeing the Interpolator's world, it becomes pretty obvious to Jim and Wilma that Quentin is doing this. They're looking at the world, making plans, while Quentin is acting out. This pulls Jim and Wilma closer together and ousts Quentin from the core group. Quentin can't appeal to the DM because there is no DM - and the Interpolator doesn't care. Quentin is alone.
The strongest punishment invoked by reality against the Quentins of the world, those who won't play well with others, is that they will end up alone and unprotected. This encourages most Quentins to at least try to play well with others situationally (though sometimes they become successful movie directors). The impress of the Interpolator's universe, both visually and in its cold-hearted nature, would encourage Quentin to 'pull together' a little if he wanted to survive the game.
True, he might still see it as a game - but with so much sensory input, he would be more easily fooled into thinking that he wasn't. This would help build a better team dynamic and thus a stronger party and game experience.
Where it comes to social pressure and the social contract, the greatest element fucking up the balance is always the DM. The DM has more power and knowledge and does not have even remotely the same motivations as the remaining players. The more personally the DM becomes invested in the outcome of the game, the crappier that outcome becomes. Removing the DM and replacing him or her with a device that can manage the other elements to a satisfactory degree (so long as the players can screw with the system to tailor it to themselves) would vastly improve the role-playing game.
How would any of this work technically? No idea. Not my problem. I'm just using this whole thing to point out that DMs need to withdraw from the system as much as possible while enacting the bare minimum of control on the players. I will embrace anything - even something that would replace me utterly - in order to better accomplish that.
Hell, if I were replaced, I could gird on my own dagger and play.