Honestly, it sounds very cool. I hope they can pull it off successfully. I just hope that they can balance giving us lots of options in mission design while not making it farmapalooza.
I also hope that, unlike a lot of other good ideas that have gone by the wayside (City Vault, CoH comic book, villain backgrounders, the Paragon Times, the fansite portal, etc. ad nauseum), that they actually follow through with taking the best arcs and making them part of the game officially.
I've been saying literally for years that user-generated content is the way to go, the Next Big Thing in MMORPGs. I was extremely disappointed when Jack Emmert said that he didn't see it happening in City of Heroes, and I'm glad that the idea was resurrected. I think that they have stumbled onto something that will make some big waves in the MMORPG market, if it is done well.