We talking what GW2 did or just setting up a bunch of NPCs that have "If by X, do this" and then just have everyone roam around?
GW2 was hidden quests with population and event based triggers, wasn't really anything 'new' except that someone actually bothered to do it. I mean, as bad as it was, WAR did the same sorta thing with PQs. In the old days you just got a ton of people together to kill a ton of stuff you otherwise couldn't, got no loot or XP and liked it... but I digress.
The thing is, worlds are static because everything is based on static events. Respawns, a few paths, etc. But you can leverage that if you add enough randomization and interactivity between entities on your own to create dynamic content. No one gives a shit about dragons that hide in a corner, so the current gen solution is to have it attack a town every 3 days or something equally retarded. How about adding a dragon that might spawn and just attack, so you know, you might not realize it's ever going to happen, or it might just not happen that way ever.
Of course people cry about not getting reliable loot, etc. But you decentralize that shit and add enough 'random' events and there's always
somethingto find/kill/loot, you just don't know what it will be based on the clock or spawn location. Dynamism through the obfuscation of arbitrarily selection and RNG leveraged against massive world size and NPC count. You just have to plan overall safeguards to keep shit from getting wacked and out of control (the cavalry, if you will) and this type of system obviously benefits from destroyable towns/cities/etc. and that type of thing...
Devs have been leveraging computing power in the wrong way. WoW has spent so much time and effort going all Michelangelo reductive sculpture and carefully crafting a million non-interacting little vignettes or quest scripts, when they should have been looking to the 'old ways' instead. Heaps of random shit on top of each other and tweak it's behavior until you have a self-generating Miniatur Wunderland instead of a connected line of 30 second quests that people ignore anyway.