This is just my opinion, I can appreciate other opinions...but this is mine.
At this point I simply do not see of MMOs. It would be far better for making an immerse world to have the player and maybe three or four friends play in a world filled with thousands of AI characters. A massive world, freedom to do what you wanted within a narrative and none of the 'ass-hattery' of other people screwing up your game. A game the runs at you pace, a world whos sole function is to give YOU an experience based on yoru own input and play style.
Sartre wrote his best-known quote in Huis-clos (No Exit), which contains the famous line "L'enfer, c'est les autres," usually translated as "Hell is other people."
Other people add very little to the experience with day's technology because MMOs run 24/7/365 with people all all at different levels all running willy-nilly all over the world. Its like a stage-play where everyone is trying to play the lead role...even if they don't want to...and all doing a piss-poor job of it. There are very few MMOs were the other people really matter, and truly the only game that uses others to the maximum benefit would be EvE. The point of other people in Eve isn't window dressing they are not the 'other elves' who make the city look lived in...they are you allies, opponents, co-workers, and MOSTLY the crumbs to be crushed under your mighty corporate thumb.
You will notice in Star Trek that the point and function of the Holodeck wasn't to have the whole ship or everyone in the Federation all playing at once in one world. The Holodeck was portrayed as an experience, often for a single individual or a small group, willing to experience something singular/special. MMOs are NOT the best way to let someone experience a world, they had a function 20 years ago to make a world seem alive, but they were/are/will be a dead end for real immersive gaming....because [whisper] other people suck. ;-)