It may be a little pedantic, but realism isn't the way to go when you're talking about games where lightning leaps from your fingertips, you mine asteroids and fly skyscraper-sized spaceships and where death is little more than a minor inconvenience.
More details doesn't necessarily mean graphical detail – World of Warcraft's graphics are hardly cutting-edge, but it doesn't seem to have slowed Blizzard down.
A more detailed MMO could have larger towns with more bustle and the sense of people buying, selling, chatting, fighting, eating and drinking – people simply getting on with their lives regardless of where I am and what quest I'm running.
I want NPCs who actually have a character, people who have a personality all of their own – I want to frequent a certain armour repairman because he recognises me and hits me with a cheesy joke every time I swing by, not just because he's the closest to the flight master. I wouldn't mind actually spending time in a bar in an MMO simply because the banter between the patrons cracked me up.
When I spoke before about crafting systems in games, I pointed out that those ideas may take a bit more computing power to come to fruition, and that may well be the case again. At the very least, too many NPCs wandering around hither and thither would obviously put a strain on system resources, not to mention the server-side power that would be required, so this is probably just 'blue sky' thinking, but if you can't daydream on a Friday afternoon, then when can you?
Just as more detail doesn't mean shinier graphics, simply adding more detail to a game may not be enough, it would have to be done correctly. I remember when Shenmue came out and much was made of the 'living world' in the game; where you could literally knock on almost any door of almost any house – it was just a shame that no-one ever seemed to be home to open said doors.
Unfortunately, because more detail and more realism are not the same things, more detail in-game may give rise to a loss of realism. With more realism in our games, they might lose some of the 'sparkle' that makes them so appealing as an avenue for escape from our day-to-day drudgery – see my previous point regarding dysentery.
Mind you, it wouldn't be all bad. With a bit more realism, some of the opposed factions in WoW might have a bit more going on between them than an uncomfortable silence. Despite the roll out of patch 2.4, and the inclusion of the Shattered Sun Offensive, the Scryers in Shattrath still seem content to use harsh language and food poisoning against the Aldor; with more realism they might manage expand their repertoire to include sharp sticks or sabotaging the Aldor Rise elevator.
Not that it needs it – if I fall to my death from that damned platform one more time, I'm going to start grinding out some Dampscale Basilisk Eyes.