This is how I see it: Several factors would need to come to play. The first is obvious, a large world, I'm talking about huge, but that's not everything...... After this designers would have to be masters of creativity far far beyond being programmers. A team of developers that goes beyond pixels and animation. Someone that can feel human emotion and capabilities.
To really live in a full world it would be designed to make the player feel "all different levels of danger". But it goes beyond that by skillful planning of giving the player the choice of when, where and how often as he wishes. A good designer would have to offer safe havens and a place to relax much like a Caveman retreats to his cave after the hunt, or as simple as two children playing outside and run inside from the rain. A warm and fuzzy. This safe haven or retreat would have to be filled with "meaningful offtakes" from adventuring like deep crafting or a true social hub much like Stormwind Castle. Sure some mmorpgs have this to an extent. But it's short, rushed, and unnatural..... "Unnatural" is the key word here.
Lets not forget, their are so many different types of people that play mmorpg's. I'll not belittle anyone by naming them all. Infact no one can....... Some of us don't know until we see it. It's a feel thing. But a good developer would have to tap into such a feel thing. Like different levels of stress then relaxed, kind of like real life. Difference being fantasy !
Wouldn't it be nice to have an mmorpg where you can escape everything ? You don't have to be a basement dweller, but a person that has a full life outside a video game with a means of retreat for leisure as long as your responsible.
What happened ?....... Back in 2004, I expected this by 2018, a WORLD-TO-LIVE-IN !! Between 1999 and 2004 was as close as we ever got. Vanguard was to be the next step but failed.