This shit isn't even being done in single player games, no way they'd do it in a mmo. Still the basics are important, day/night cycle, randomized weather, that kind of shit is pretty cool and has been done so it can be done again. The theme park mmo concept isn't just the mechanics design of doing quest hubs and localized monster areas and linear progression etc, it's also the feel of the zones. WoW zones are always the same. They each have a unique identity made by using color scheme like int he sky and most elements and shit like that, but if you go to ashenvale it's always the same ashenvale, there's never an ashenvale by day or ashenvale by night or ashenvale when it's raining and that makes it feel very artificial, especially when it's connected to the fucking barrens. Having day/night cycle and weather(not necessarily advanced weather but like, cloudy, rainy, snowy maybe) you can go to a zone and level there for a bit and suddenly night falls and it's like an entirely different zone. Then it starts raining and it's like "motherfucker I can't see shit". That peaceful plain area becomes an oppressive scary area just by adding a few modifications.
Wish more mmos did that shit. PS2 has day night cycle so it should be the same I hope, just wish they add weather stuff too.