Emergence is one of the aspects that many MMOs aspired to, only to drop in favor of static storytelling. The problem with emergence is that simple decisions would have a compounding impact on the world. Heroes would solve problems, only to perhaps create further problems with their implemented solutions. Most game architecture can't handle decision making of that nature, as it would need developers to constantly code in the new events that would occur.
However, Heroes of Telara seems to be aspiring to that using server-side gaming. Their proposed method, as it appears in an interview between Trion's CEO, Lars Buttler, and GamesIndustry.biz, is to run the game entirely server side, letting developers change and alter the game on the fly. As Buttler puts it, "There are small events, there are big events, there is even emergent behaviour in the game that changes the game world. A lot of it is not even known to us, it's like the ghost in the machine. The game is almost alive, and that allows you to create heroes."