I've been thinking of what kind of setting and player customizations I would want in an MMO. I feel that when thinking of a game, the story should come first, and then you can build the mechanics around the story. Even if all you have of the story is a single phrase.
"Mechanized world, where three factions have splintered to control the world."
The idea is that you would create the society first and split it from there. I'd split it as Renegades, Enforcement and Scientists.
Players choose a faction, which determines parts and style available to make their avatar. The avatar would be a modifiable robot. The game would not have any leveling up. Everyone would begin with standard gear. New gear that is found would have positives and negatives balancing each other out, i.e.: this laser is more powerful, but causes you to overheat.
As you customize your avatar and decide on his weapons, armor etc., you would also have macros designed to cause special effects with your weapons. These programs would be part of the gameplay (concept is still being worked on, I might reveal more later).
The question becomes, what are you willing to sacrifice to function a certain way? I'm not sure how big this game would get, but I can see flaws already in here.
But, are the things that I see just things that really don't work, or are they things that are so different from the current MMO or RPG models, that I don't know how to work with them?
Other things come to mind, such as showing that someone is improving (I mean, with equal negatives, it is assumed that you are just as functional as a neutral person), or giving a sense of progression (with a game designed for everyone to be able to play right from the start, how do you show progress?).
These are answers for a different time, for now, lets think of what combat systems would give us the most options of giving negatives to the player so that we can give them more benefits. I immediately thought of a skill based combat system, where you could allow for targeted attacks be giving up some power, or give your attacks more aggro by increasing the base damage. By having your attacks require scaling for damage, you would negate the aggro, but require more stat manipulation to get the attack's damage up. There is a great deal that can be done here, and not much more unless we design some stats to track.
Finally, we can attach an element system to this (perhaps a modified Chaos system). All these interesting game decisions came from a story idea, and I think it makes for the most interesting design decisions. Have I mentioned crafting yet? No, but you could easily see how getting parts from defeated machines would work out (especially when using Chaos as the element system). So there you go. The beginnings of a game.