I actually implemented my random idea (not to the full degree I wanted) as a NWN mod that ran as a persistant server (like a small MMO) and the players enjoyed the hell out of it. Nothing has to be the same. And nothing was the same.
Easier said than done. MMO's have to be great and realistic games, but have to be the same game for each player. That means that the questgivers will stand in the same spot 24/7 and the quests will have to be text-based, and there are lots of queues.
I scripted everything up to cater to the individual player instead of what MMOs do, which is have set things stand there 24/7 and make the player cater to the preset content.
In a standard MMO there is a static broken merchant caravan at the same spot. The NPC will stand there 24/7 and repeat the same crap about the same guys that ran off to the same place over and over again. The enemies drop the same crap over and over, and there is one thing you can do with it.
In my system, there was no cart, there was no quest. I gave every player an array of 3 quest slots as part of their custom data, and I generated stuff on the fly to fill those empty slots.
So a player enters a zone. This zone has part of a road that goes from town a to town b. So it's a trade route. So after checking that the player has an empty quest spot, and he passes a random check to see if I should generate something,
I generate a merchant cart somewhere. Not on a specific pre set spot. Anywhere in the zone. In the grass, up a tree. Upside down in some rocks. Who cares? Just put it somewhere random. If the player stumbles upon it, then his imagination can fill in the blanks. The thieves hid it, they ran him off the road, or the merchant was drunk.
Maybe I generate a merchant there with randomly generated story that some (creature/guild/thieves) attacked him and ran off with (any random item).
Maybe I don't generate a merchant, and I just put some random object there that acts as a clue that (random creature) was there and ran off to (random place).
Maybe the merchant is fine and YOU decide to act as the bandit, creating new content for another player to find.
So now the player has a unique event to react to or ignore.
When the player enters the destination that has the (random creatures), I see this in the script that checks everyone who enters a zone, I generated the content for them.
If the player destroys the (creature) and gets any randomly generated associated loot. He can do what he likes with them. There are variables attached that say what they are, and where they came from. So the game always knows that player has the loot item from a bandit raid on the road (should he choose not to return it), and the game can react to it constantly. Maybe you don't want to return it because you're evil, it's useful to you, or you can get a better deal for it).
On rare occasions, that loot could have been an item someone else was looking for, causing new random quests between the factions that were interested in it.
If a another player stumbled upon that merchant that was waiting for the loot return and killed him. I'd generate an evidence item. So you'd have the loot to find a new owner for, and a quest item to find out who who murdered that guy (if you wanted to follow up on it). (I never coded up the part where I wanted this to happen only with nearby players, and to require the player to interact with them as witnesses, then the guilty player can have generated authorities looking for them).
I had quests to save NPCs from randomly generated places or villains. You could return them. Rob them. Beat them. Return them by demanding a ransom. Sell them to slave traders. Sacrifice them to some evil deity, etc... It was all up to the player.
What happens if a large chunk of players are sacrificing or selling into slavery? The game keeps track of this. So it can react by spawning appropriate content.
The cult of the evil deity is growing stronger. So spawn a higher percentage of followers. The town NPCs are spawned with pitchforks, clubs, and torches. They generate quests and jobs that are weighted towards cracking down on this cult or freeing slaves.
Those merchants you bump into aren't getting robbed now. They are afraid of the cult and need your protection! They are afraid to walk alone, or you can't let their deliveries get into the hands of that cult. Are you in that cult? Then you just found your next sacrifice alone in the woods.
Everything was random and flexible and apart of the same system. Everything was aware of the state of the world and could react to it and change it. Everything that happened could change the state of the content for the other players and it was player driven to begin with.
I hacked this up in my basement when I was 22 and knew half of what I know now. I'm sure a bigger, real MMO could try something similar. You just need a little data structure that says who/what/where/why/when and then to make everything aware of it. Even NPC chatter can be gossip about player deeds.